108 [Assembly 



Of the Cephalopoda of the Upper Helderberg* group, four species of 

 Cyrtoceras and one Phragmoceras have been described, viz : G. para- 

 doxnm, G. trivolvis, G. matheri, G. undulatum, and Phragmoceras spino- 

 sum. Several species of Orthoceratites and Gomphoceras are known, 

 and two of Trochoceras. 



, di{ 



TROCHOCERAS CLIO (n.s.). 



Shell discoid or depressed, snborbicular, convex above and 

 broadly umbilicate beneath : volutions about three, gradually 

 ♦ expan^ding, the last one becoming ventricose ; the outer cham- 

 ber large. On the lower side of the outer volution, where the 

 diameter is half an inch, .the septa have a distance of about 

 one-tenth of an inch ; while in the margin of the umbilicus at 

 the same pail;, they have not more than half this distance, and 

 upon the dorsum about one-eighth of an inch. Siphuncle 

 central. 



Surface strongly annulated upon the upper and dorsal portions . 

 of the volution, the ridges dying out in the umbilicus : entire 

 surface evenly cancellated by transverse and revolving striae. 



This- species attains a diameter of two or three inches, and can be 

 known in its fragmentary condition by the annulated surface. 



Geological formation and locality. In the Schoharie grit : Helderberg • 

 mountains and Schoharie. 



TROCUOCERAS EU&ENIUM (n.s.). ^ 



Shell subhemispherically discoid Evolutions strong, gradually 

 increasing from above to the last one, which becomes more 

 rapidly expanded and ventricose ; outer chamber large. Septa, 

 where the shell is one inch iji diameter, onfe-fifth of an inch 

 distant on the lower side, gb-nd about half the*^me distance at 

 the margin of the umbilicus : volutions a little flattened upon 

 the lower side, and abruptly curving into the deep umbilicus. 

 Siphuncle dorsal : dorsal surface of casts showing no annula- 

 tions ; character of shell unknown. 



