24 Talbot — New York Helderbergian Orinoids. 



be referred to this genus is found in one of the beds of the 

 Coeymans limestone at North Litchfield. The generic features, 

 as given by Wachsmuth and Springer,* are well marked — the 

 subglobose calyx, urn or bell-shaped ; infrabasals five, small, 

 barely protruding beyond the column ; basals five, the posterior 

 one truncated by a large anal plate ; radials Hve, considerably 

 larger than the costals ; costals two ; arms ten or twenty, rather 

 strong and biserial ; pinnules long ; first interbrachial large, 

 followed by smaller ones ; anal side wider, first anal plate fol- 

 lowed by three in the next row. 



The specimens under examination lack the ridges which are 

 so conspicuous in marking the rays in most of the species of 

 Thyscmocrinus ; their plates are smooth, instead of being 

 sculptured as is generally the case in this genus, and the column 

 is pentangular, while in most of the species it is round. The 

 specimens resemble T. liliiformis more closely than any other 

 species, but differ from it in the pentangular column and the 

 absence of the ridges on the radial series of plates. Not enough 

 is known about the bifurcation of the arms in T. liliiformis 

 to make comparison. 



Specific description. — Calyx subglobose. 

 Surface of plates smooth. Infrabasals five, 

 small, projecting slightly beyond the col- 

 umn. Basals five, large, hexagonal, the 

 posterior one heptagonal and truncated 

 above to receive the anal plate. Radials 

 five, somewhat larger than the basals, pen- 

 tagonal. Costals two, half as large as the 

 O radials, hexagonal, the second smaller than 



^s^+y the first and supporting on its sloping upper 



| _j f^) margins the two rows of distichals, the 



^^ lower three of wdiich are larger than the 



C^J succeeding ones and are embodied in the 



. _ I) . calyx. Interbrachials, two ranges of large 

 graiTof Thysanocrinus plates followed by smaller ones. Anal 

 arborescens showing plate large, followed by three much smaller 

 position of the anal ones [ n ^h e nex £ row> Arms biserial. Each 



plates and first bilur- i -n , , T -, , -, -j 



cation of the arms. ra J bifurcates on the second costal and 

 again on the fourteenth distichal. A third 

 bifurcation occurs, seemingly only on the inner branches and at 

 different intervals in the different arms, varying from the four- 

 teenth to the twenty-third palmar. Pinnules found on the fifth 

 distichal and continuing to the tips of the arms. Column 

 pentagonal. Near the calyx, the joints alternate in size ; but 

 farther down the stem every fourth joint is larger. In a speci- 

 men in which the crown is 29 ram in length, the column, though 

 incomplete, is 40 cm long. 



*N. Am. Cri. Cam., vol. i, p. 190, 1897. 



