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vol. iv. pi. 5. f. 10), rather than to that by Mr. Bell ; because the latter, though I have no doubt correct to the specimen, appears not to express adult proportions ; but implies at some more advanced period of its growth, a sudden lateral expansion. The arms, however, are of the full dimensions; and the spines and straightness of the anterior border of the carapace, are expressive of the species. My specimen of G. angulatus measures 1½ inch across, and ¾ of an inch in length ; which is very nearly the proportion of Pennant's figure ; and in this specimen the anterior limb measures rather more than four inches in length. At that portion of the carapace which in G. angulatus forms the strong advancing spine that affords the specific designation of Pennant, in G. rhomboides there is only a gentle curvature, that makes no approach to the nature of a spine ; and there is no appearance of that second lateral spine, of which in its congener there is always a rudiment ; and from which Dr. Leach seems to have derived his name, G. bispinosa ; but which is too powerfully given on the right margin of Pennant's figure. This hinder spine is somewhat strangely omitted on the left side of his specimen. The eye-stalks are more curved, as is also the margin of the carapace that conceals them, than in undoubted specimens of G. angulatus ; and as they lie hid, the joint is anterior to the ocular portion : a circumstance which induced me, in the Cornish Fauna, to place this species in the genus Gelasimus, under the name of G. Bellii ; in honour of the professor of Natural History in King's Col- lege. My past observations of this species having been confined to female specimens, a greater degree of uncertainty has formerly prevailed in my mind concerning this crab ; either as regards the distinction of species, or the progress of evolution of its form ; for while in a male G. angulatus of the dimensions already given, the arms are four inches in length, it is known that the same parts in the female are very much shorter, as well as more feeble, a rule which, indeed applies to all the species of crustaceans. But my present account is derived from an undoubted male specimen of G. rhomboides ; in which I find their length to be proportionally much shorter than in the kindred species ; and their appearance to bear a closer resemblance to the same parts in the female in the other. On the arm, where in G. angulatus there is a spine, in this there is a very slight mark of a point ; and a portion of the carpus is only mem- branous : although this last may be a defect confined to the individual. In the interior lengthened portions of the smaller legs of G. angulatus, there is on the superior ridge, where it is about to terminate in the tarsus, a small, but well-marked spine; which in the present species is absent, the place being marked by a depression, followed by a rising. Mr. Bell, in his description, says that in the young male of G. angulatus, the arms resemble those of the female ; and from this circumstance it may be objected that one of the most distinguishing marks of this as a species, will be of less importance. In all other cases, however, T have found that when the flap or tail has distinctly assumed the male form, all the other organs have also adopted their permanent condition. The margin of the carapace may at least be judged to have done so ; and yet this, in so large a specimen, preserves the well marked distinction from the other. If then, the Gonoplax rhomboides be allowed to be a distinct species, it must be claimed as scarcely a rare inhabitant of the channel, where the present specimen must have lived at the depth of thirty-six or forty fathoms. If it be otherwise decided, there is room for further research, to discover the progress and proportions of its development; and whence it happens that it observes a law so very different from that of other British crabs. I have generally failed in obtaining good specimens ;

for though G. angulatus has sometimes come within my reach alive and uninjured, I