sity 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[1] 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
- ↑ Schuchert., Charles. On Siluric and Devonic Cystidea and Camarocrinus, Smithsonian Miscellaneous Collections, Part II. 244. 1904.
