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It is valuable, m that It will keep alfo, and Is a very proper form to keep ifing-glafs in, for readinefs for the wine-cooper's ufe ; befides this ' it ferves alio very elegantly for the taking off the impreihons of medals, coins, &'c. Show's Lectures, p. 430. See the article Medal. Ic'hthyocolla Pi/cis, in zoology, the name of a large fifh of the fturgeon kind ; from which, as alfo from the tiujo Germanorum, the drug called iiinglafs or Ichthyocolla is made. It is a fifh of very great fize, and is cartilaginous, having no bones nor fcales. Its head is large and thick, and its mouth fl-ands very forward. The upper jaw has four fiefhy apo- phyfes hanging from it. Its eyes are fmall : Its flefh is very well tailed, but glutinous. It is of a yellowifh colour, and its tail is large and forked. Willughbys Hilt. Pifc. p, 244. ICHTHYOLOGY, the fcicnce which treats of fifties. The proper objects of this itudy are aquatic animals, which have fins, and have no feet. The bulinefs of Ichthyology is, firft to diftinguifh all the parts of fifties, by their feveral proper names ; then to adapt to each fifh its proper generical and fpecific names ; and finally, to commemorate fome of its peculiar qualities. The naturaiifl: wfio ftudies fifties, is firft to examine the feveral parts, as well internal as ex- ternal of the animal under confideration, and be able to treat of each under its proper denomination ; then to refer what- ever ftrano-e and unknown fifh is brought before him, to its proper family ; and on examining its near characters to bring it to the genus of that family to which it is found to belong i and by conhdcring its parts, with the defcfiptibns authors have given of the feveral fpecies of that genus, to find by compa- nion which it moll fuits, and therefore of which fpecies it is. This done, the fifh is known. After this, by fubfequcnt " obfervations, he is to find out its place of habitation, whe- ther in fait pr frefti, m running or ftanding waters. Its food whether animal or vegetable, and of what kinds ; and its time and manner of propagating its fpecies, and bringing forth its young. Theie lait particulars are to be added to the defcription of the parts of the fifh, in few words, for Ion* and diffufe narrations of this kind ferve rather as a load than an inrtruction to the judicious reader; and the true and natural method in the genera and fpecies of created things, is the true intent and end of natural fuftory. Arted'i Ichthyol. p. 3. See Generical Name.
The general divifion of fifties is into three claffes ; the ceta- ceous, the cartilaginous, and the fpinofe. The cetaceous fifties are thofe whole tail is fo placed that when the fifh is in its natural pofture, it flands parallel to the horizon. The cartilaginous fifties are thofe whofe fins ferving for fwimming are fuitained by cartilages in the place of the bony rays which fupport them in the other, and which have alfo cartilages in the whole body, inltead of bones. Thefe are the characters off the two firft claffes ; and all thofe fifh which have their fins fupported by bony rays, which have their tails placed perpen- dicularly, not horizontally, and which have bones not carti- lages in their bodies, are called the fpinofe fifties. Thefe are the diviiions of the fifh in general arnon^ authors. The cetaceous fifties are arranged together, by the later wri- ters on. natural hiftory, under the name of Plagiuri. Thefe agfee' in, many things with the land animals, and are diftin- guifhed from one another by the fame characters which feivc for the diftmction of the quadrupeds, particularly by the teeth. The general ftructure of thefe fifties is alike in all ; and their only differences are . in the teeth, and the number of fins. From the teeth and fins, alone therefore, are to be properly taken the geiK.ical characters of the Pla- giuri'. Artedl fchthyolog.
The cartilaginous fifties differ from each other only in the fupn of their body, and in the number of the foramina of the bronchia. For the number of the fins, and figure and pofition of the teeth, which in the former plate make the on- r ly characters of generical diflinctions, in thefe are fo variable, that th'ey frequently differ in the different fpecies -of the fame genus. The 1 characters for the diftinction of the cartilagi- nous n&es Intjo genera, can therefore only be taken from the ftiape and foramina. Thus all' the rays have flat or de- preffed bodies, and five, foramina at the bronchia. All the 'pettomyzse have, 'on the contrary, rounded bodies, and feven foramina at the bronchia. The chonepterus and mala have rouiidifb. bodies, and only one foramen or hole
- for the bronchia j and fo or the reft. The feveral fpecies of
the rays, tho' all properly belonging to the fame natural ge- nus, yet differ greatly in their number of fins, and in the ftiape and difpqfitioii of their teeth. '
The true characters of thefe two great claffes of fifties, the cetaceous and cartilaginous, are thus eafily found ; but the characters of the fpinofe kinds are to be fought for deeper, and do not offer themfelves, fo readily. The multi- tude of tliefe, 'and the great likenefs between feveral of the different genera, 'render it no eafy lafk to diftinguifh them \ one from another. Though it be a general rule that the - generical characters of fifties are to be taken from their ex- " terhal parts ; yet in cafes where thefe external parts differ in _ theirvfelves in number, figure, and proportion, it is neccftary that the prjnwv character of the genus fnould be taken from thofe parts which are the" Icaft variable of all others ; and 3
which are the moft peculiar to the fifh under confideration, and the leatt common to -other genera. The utmoft care and fkill of the Ichthyslogijf is neceilary to the diftinguifhiug thefe characters ; and on a ftrict enquiry he will .find, that thofe parts which feem at firft. moft proper to found diftinc- tions on, are in reality leait of all fo. The figure of the fins and tail in fifh might feem one of the moft effential characters tor a generical distinction, yet a farther fearch into their nature will fliew that they can-be of no ufe at all in this fenfe. Almoft all the fpecies of the cyprini, a genus constituted on effential and invariable characters, and a tru- ly natural one, have fins" acute at the end, and have forked tails; yet had thefe been' made characters of the genus, they would have excluded fifh that are properly of it. Thus the tench and the carailius have born obtufe fins, and tads ftrait or plain, not forked at the end. There are indeed many natural genera of fifties in which the fins and tail are alike in all, as the pearch, the mackre), the conger. Thefe allow the fins and tail as very good col- lateral circumltances of the distinction ; but even thefe could not well be diitinguifhed by fuch marks alone, as they are common to many other genera befides. The figure or the breaft, the belly, and the back, and the whole figure of the body in regard to length and breadth, are all very obvious characters ; but they are not effential enough to be of any ufe in the distinctions of the genera. The back in fome of the cyprini is Subacute, as in the com- mon bream ; whereas in almoft all the others, it is only mo- derately convex. This fets aiide the ufe of the figure of the back as a generical character, fincft the bream, notwith- ftanding this difference horn the reft oi the cyprini, is truly of that genus. The belly, in the far greater number of the cyprini, alfo is plane in the anterior part, and between the pinnx ventrales and the anus is railed into a ridge ; but in the tench, the whole belly from the head to the tail is flat. And to this it may be added, that the general figure of the body, as to length or breadth, is extremely different in the cyprini of various fpecies, as witnefs the bream, the albur- nus, the rutilus, f&e'. fome of which are properly fiat, and others almoft round.
The figure of the head, the mouth, the eyes, the noftrils, and other- parts belonging to the head, are very different from thefe variable parts ; tfiey are in general fixed and per- manent, and are of the utmoft confequenee in the diftinc- tions ; but as this figure is too common, and belongs to too many fpecies equally, they are rather of ufe in the diitin- guifning the orders, claffes, and families of fifties, than their genera. Thus the clupea?, the cotti, the coregones, and fcor- pamae of authors have a plain genera! refemblance in the form of their heads, and yet they are of very different genera. The figure of the fcales is generally always the fame in the fame genus, and therefore may be made a good collateral circumftance in the diftinetions ; but as the fame form is common to the fcales of many genera, it is impofiible to bring them to any great ufe in the constituting the characters of the genera. As to the fituation of the external parts, as that of the eyes, noftrils, mouth and anus, they are generally regular and alike in all the fpecies of the fame genus, re- gard being had to the proportion ; but as their fituation tho' alike in thefe genera is not peculiar to each, the marks are too common to be ufed as diftinctive characters for ge- nera. The fituation of the fins alfo is ufually very regular- ly the fame in all the fpecies of the fame genus ; but the fame objection lies againft this as againft the others, in regard to ' making generical characters from it. The clupeae, the coregones, the falmons, and cobitides, every body muft al- low to be very different genera of fifties ; yet in all thefe the fins are placed in the fame fituation. The pectoral fins in all thefe ftand nearelt the head, the neareft next to thefe is the back-fin ; after this come the ventral fins, and behind all the reft the pinna ani. The fame obfervation will alfo hold good in feveral other genera, which have thefe and other marks in common. The fituation of the fcales of fifties, in regard to their denfity or rarity, always holds the fame in the feveral fpecies of the fame genus ; but this alfo is a mark common to many genera. The fituation of the teeth agrees in the fame manner in all of the fame genus, and in many genera. All the cyprini have their teeth placed in the fame order and manner ; they all ftand in the fauces at the orifice of the Stomach. The falmons and pike have their teeth in four places, the jaws, palate, tongue, and fauces. The pearch, the cotti, and clarise have them in three places, the jaws, palate, and fauces; but not on the tongue. But among the coregones, one fpecies, the albula nobilis of Schonfield, has the teeth in three places, in the up- per jaw, the palate, and the fauces. Another fpecies, called by the Swedes the filk-joia, has them only in one place, which is on the tongue ; and another fpecies of the fame ge- nus, the thvmallus of authors, has them in both jaws, in the palate, and on the tongue. Therefore it is evident, that no generical character can be eftablifhed on them. The num- ber of the teeth can be of no ufe in the making characters of genera; for this very often varies in the fame fpecies in different individuals, as in the pikes, falmons, fif*. The
number
