TROOST'S CRINOIDS OF TENNESSEE — E. WOOD. 99 



Order FLEXIBILIA Zittel. 



Family ICHTHYOCRINID^ Bather. 

 Genus ICHTHYOCRINUS Conrad. 



ICHTHYOCRINUS TIARiEFORMIS (Troost) Hall. 



Plate 7, figs. 15, 16, 17. 



Cyathocrinit.es tiarseformis Troost, Proc. Amer. Ass. Adv. Sci., II (read 1849), 

 1850, p. 60 (nomcn nudum); MSS., 1850. 



Ichthyocrinus tiarseformis Hall, Rept. Geol. Surv. Iowa, I, Pt. 2, 1858, p. 558. — 

 Shumard, Trans. Acad Sci. St. Louis, II, No. 2, 1866, p. 378 (catalogue name). — 

 Wachsmuth and Springer, Rev. Palseocrinoidea, I, 1879, p. 35. — Miller, 

 North Amer. Geol. and Pal., 1889, p. 256 (catalogue name). — Weller, Bull. 

 No. 153, U. S. Geol. Survey, 1898, p. 312 (catalogue name). 



The description by Troost is as follows: 



When I discovered this very perfect specimen I put it down as belonging to a new 

 genus, as I found, or at least thought I found, nothing analogous to it in Miller or 

 Goldfuss, I was therefore surprised when I got possession of Murchison's "Silurian 

 System" to find a fine figure and description by Phillips of the Cyathocrinites [Ichthyo- 

 crinus] pyriformis, which, except in some specific differences, coincides with the 

 fossil under consideration. I am glad nevertheless that Phillips himself says — "but 

 in Miller's technical arrangement it ought probably to constitute a new genus." — It 

 is therefore only necessary for me to mention in what respect it differs from the C. 

 pyriformis. 



Its difference in general dimensions is pretty considerable. The C. tiarseformis is 

 30 mill. m. long by a diameter of 35 mill, m.; the dimensions of the C. pyriformis 

 taken from the figure in Murchison is 20 mill m. long and 15 mill. m. in diameter. 

 The cicatrice for the column in the tiarseformis is about 8 mill. m. in diameter whereas 

 that of the pyriformis seems hardly one-fourth of this dimension. In the pyriformis 

 the pelvic [basal] plates do not project beyond the diameter of the column [?] and 

 increase only slightly together with the costals. — In the tiarseformis on the contrary 

 the pelvis [base] projects considerably beyond the column, the diameter of the 

 column being 8 mill. m. while that of the pelvis [base], taken from one of the angles 

 to the opposite edge is 11 mill. m. and increasing more rapidly in diameter at every 

 series of successive plates till it terminates almost abruptly and forms an almost level 

 summit which gives it somewhat the appearance of an oriental turban, (tiara from 

 which its name). 



But it differs still more from the pyriformis in the subdivision of the hands, we see 

 on the figure of the C. pyriformis (Sil. Syst. pi. 17, fig. 6) that it terminates at the 

 summit in 40 fingers, whereas, as appears from my figure, the tiarseformis terminates 

 in 20 fingers. 



I discovered it in Davidson County, Tennessee, near White's Creek Springs amongst 

 the disintegrations of the Carboniferous and Devonian strata. It is changed into 

 silex like most of the fossils of this locality. I found only one specimen, and it being 

 without blemish it forms one of the ornaments of my collection. I never understood 

 that even a fragment of it was found, so that it must be very rare. 



Observations. — In Hall's description of this species [1858 p. 558] he 

 speaks of the "absence of basal plates," but Troost's desciption 

 emphasizes the projection of these plates beyond the column. Mr. 

 Frank Springer who has the type in his possession assures me that 



