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NEW YORK STATE MUSEUM 



nized by its almost cylindric and very slender form ; O. pravum 

 [fig. Ill], distinguished from the preceding by its larger size and 

 widely separated septa and O. (Cycloceras ?) thoas 

 [fig. 112], a cylindric annulated species, with deep camerae and 

 moniliform siphuncle. 



Among the cyrtoceratites, or curved cephalopods, Cyrto- 

 ceras (Rhizoceras) eugenium [fig. 113] easily ranks 



Gyroceras spinosum [fig. 114], which is easily known by 

 the spinose ventral ridges and the additional row of tubular 

 spines on either side of the venter. The torticones, finally, or 

 those in which the coil is not in a single plane are represented 

 among many others by T r o c h o c e r a s c 1 i o [fig. 115], a left- 

 handed or sinistral loose coil of about three volutions which 

 enlarge gradually and leave a moderate umbilicus at the base, 

 while the surface is marked by numerous, rather faint, rounded 

 annulations crossed in well preserved specimens by sharp longi- 

 tudinal sirlae. T r . (Pteroceras?) eugenium [fig. 116], 

 in which the whorls expand more rapidly than in the preceding 

 and the surface is free from crenulation, is also among the more 

 common species of this type. 



Fig-. 116 Trochoceras eugenium 



first in point of abundance. It 

 is a long, slender form with a 

 gentle curvature and slightly 

 elliptic cross-section. The sur- 

 face is marked by regular and 

 prominent foliate ridges or ex- 

 pansions of the shell which 

 are strongly deflected back- 

 ward in a hyponomic sinus on 

 the ventral or outside surface 

 of the curved shell. Between 

 the folds' are fine transverse 

 and longitudinal striae. The 

 gyroceracones or loose-coiled 

 nautiloids are represented by 



