Lipsanocystis traversensis, a new cystid from the Devonian of Michigan
A NEW CYSTID, FROM THE DEVONIAN OF MICHIGAN
G.M. EHLERS AND J.B. LEIGHLY
[Reprinted from the Papers of the Michigan Academy of Science, Arts and Letters, Vol. II, 1922]
LIPSANOCYSTIS TRAVERSENSIS, A NEW CYSTID FROM THE DEVONIAN OF MICHIGAN
G. M. EHLERS AND J. B. LEIGHLY
In the Museum of Geology of the University of Michigan there was recently found a cystid with a label, in Dr. Carl Rominger's handwriting, bearing the name Lepadocrinus hamiltonensis Rominger, and indicating that the specimen was collected at Partridge Point, Thunder Bay, Michigan. This cystid is probably the one that Rominger had in mind when he recorded the occurrence of the genus Lepadocrinus along with several genera and species of corals, echinoderms, bryozoa, brachiopods, and trilobites in the rocks of Partridge Point, which he regarded as belonging to the Hamilton group. No description, however, of this cystid, or of the species Lepadocrinus hamiltonensis Rominger, occurs in the literature. It seems very probable that Rominger, after recording this occurrence of Lepadocrinus, thought the cystid to be a new species, labeling it Lepadocrinus hamiltonsis, never publishing a description of it.
Upon examination, it became evident that this cystid did not belong to the genus Lepadocrinus.(=Lepocrinites), but to an undescribed genus, for which the name Lipsanocystis proposed.
Lipsanocystis, n. gen.
Definition.—Apiocystinae with 20 plates, arranged as follows:
Plates, 4, 1, 2, 3, in basal row;
Plates 3, 6: 7, 8, 9, in second row:
Plates 10, 11, 12, 13, 14, (15), in third row;
Plates 16, 17, 18, (13), 19, 15, in fourth row;
Deltoid 23 double, in fifth row.
Deltoid 23 is double, and contains both the madreporite and the hydropore. The former is divided, and appears as two elevations, each with an orifice in its apes. The hydropore appears as a small circular opening below and between the two parts of the divided madreporite.
Anal opening moderately large, entirely enclosed by plate 13, except for about 2 mm of its periphery, which is formed by the upper edge of plate 8. One basal and 2 upper pectinirhombs, with numerous dichopores, situated respectively on plates 1 and 3, 14 and 15, and 12 and 18. The halves of the pectinirhombs on plates 5, 14, and 12 surrounded by conspicuous raised margins, those on 1, 15, and 18 without mariginal walls.
Ambulacra four, simple, extending to the basal row of plates. These are RI, RII, RIV, and RV. Brachioles relatively few in number and rather widely separated.
Genotype, L. traversensis. No other species known.
Lipsanocystis shows in its structure relationship with other Apiocystinae, especially Apiocystites and Tetracystis. Dr Charles Schubert, who has examined the specimen, pronounces it "a changed Apiocystites, having become more depressed and therefore has changed somewhat the arrangement of the plates." It has pectinirhombs resembling somewhat those of Tetracystis chrysalis Schuchert, but differs from all other genera of the family in having the anal opening almost entirely enclosed by plate 13, only a small part of the border being formed by plate 8. (See Text Fig. 5.) Since this genus is apparently a holdover of a Silurian type, the name Lipsanocystis is given to it.
Lipsanocystis traversensis n. sp.
(Plate X, Figs. 1-5, Text Figs. 4, 5, 6)
Greatest length of theca of holotype 22 mm.; greatest width 19 mm., thickness 15 mm. Form and appearance of entire theca shown in Plate, X, shape of individual plates in diagram, Fig. 4.
Fig. 4. Diagram of thecal plates.
Ambulacra prominent, occupying extremely shallow grooves in the thecal plates. Brachioles 14 to each ambulacrum, or 56 to the entire theca. Length unknown.
|Fig. 5. Sketch of anal side, showing relationship of anal opening to adjacent plates. x 2.||Fig. 6. Diagram showing probable outlines of plates composing rows 4 and 5. Parts covered by ambulacral plates stippled.|
Pectinirhomb on plates 1 and 5 has about 45 dichopores, that on plates 12 and 18 about 42, that on plates 14 and 15 about 50.
Anal pyramid unknown.
The single specimen, No. 5414, Museum of Geology, University of Michigan, upon which this description is based, is from the upper part of the Thunder Bay division of the Traverse formation, at Partridge Point, Alpena County, Michigan. Since the name Traverse is now applied to the formation from which this fossil was collected, the specific name traversensis is used instead of Rominger's hamiltonensis.
The description above is based upon a single specimen in the Museum of Geology of the University of Michigan. The details of the oral parts are masked by the ambulacra. A conjecture as to the form of the plates thus partly covered is shown in Fig. 6, in which the parts of the plates covered by the ambulacrals are stippled. The two upper circles on deltoid 23 in this figure are interpreted as a divided madreporite, with the hydropore appearing faintly just below and between parts of the the madreporite. These latter parts are elevated, and in appearance closely resemble the adjacent bases of brachioles. They are connected by an elevation above the surface of the plate, and are interpreted as the madreporite on the basis of their apparent similarity to the structure described by Schuchert in Callocystites jewetti "Madreporite ∞-shaped and situated on the two parts of plate 23. Hydropore immediately beneath the madreporite, very small."
There is some doubt concerning the relationship of a small part of the theca situated orally from plate 15, and anteriorly from plate 19. This may be interpreted as a part of plate 19, a part of plate 15, or perhaps as deltoid 20.
Another doubtful detail is the form of plates 10, 13, 15, 16, 17, and 23. The hypothetical completion of the plates in Fig. 6 is based upon the apparent position of the angles of the plates as indicated by the intersection of the visible parts of their sides produced. The doubt concerning these structural details can only be resolved by the examination of additional material.
University of Michigan
EXPLANATION OF PLATE X
Lipsanocystis traversensis, n. sp. (Natural size)
|Fig||1.||View of anal side of theca. Upper part of ambulacrum RV missing.|
|Fig||2.||View of antanal side.|
|Fig||3.||Oral view of theca. Deltoid 23 with divided madreporite appears immediately at left of mouth opening.|
|Fig||4.||View showing the upper left-hand pectinirhomb and the configuration of the ambulacra. Anal side to the right.|
|Fig||5.||Opposite side to that shown in Fig. 4, showing upper right-hand pectinirhomb and fragment of column adhering to basal plates.|
Lipanocystis traversensis. n. sp.
- Rominger, Dr. Carl, Geology of the Lower Peninsula, Geological Surey of Michigan, 3: Part I. 41. 1876
- The writers wish to express their appreciation of the kindness of Dr. Schuchert in examining the fossil and offering valuable suggestions as to its structure and relationships.
- Schuchert., Charles. On Siluric and Devonic Cystidea and Camarocrinus, Smithsonian Miscellaneous Collections, Part II. 244. 1904.