452 PALEONTOLOGY OF ILLINOIS. 



several in the collections of Messrs. Springer and Wacfismtjth. It is 

 especially distinguished by the erect or strong forward curvature of the 

 external body, the sharp anterior margin terminating below in the 

 broadly expanded aud slightly convex though laterally sharply defined 

 anteroinferior shoulder, which, instead of being notched in front, grad- 

 ually narrows and slopes into the superior basal edge, terminating in a 

 blunt point; the lateral surfaces are traversed longitudinally and nearly 

 centrally by a distinct groove, transverse section near the middle sub- 

 lenticular, the posterior face moderately channeled by the exposed 

 pulp cavity. The largest specimen was probably above an inch in 

 length. 



Physonemus depressus. 



PI. XVIII, Kg. 3. 



Is represented by a few imperfect specimens, also from the lower fish- 

 bed, which are particularly recognizable by their larger size, depressed 

 position or comparatively gentle curvature, the anteroinferior shoulder 

 broadly rounded from side to side, notched in front and produced 

 anteriorly into a long, slender point; transverse section similar to the 

 preceding form, perhaps less sharply rounded in front, and moderately 

 excavated by the open pulp cavity behind. Length of the largest 

 example above two inches. 



Physonemus carinatus. 



PI. XVIII, Fig. 4,5. 



Two fragments of spines from the upper fish-bed of the Kinderhook, 

 preserving the inferior portion, are the sole representatives of the pres- 

 ent form in the collections. The spines were probably near the last 

 above mentioned in form and position, and especially characterized by 

 the more or less laterally compressed and keeled anteroinferior shoulder; 

 more or less deeply notched in front and produced anteriorly, and in 

 transverse section laterally more compressed than is the case in either 

 of the above named forms. Iu size the specimens here referred to prob- 

 ably attained the length of two inches. 



With the material in hands, however apparently well defined the 

 forms mentioned above, we are not prepared to express an estimate of 

 the value of the characters upon which they are founded, nor can this 

 be ascertained without the aid of larger collections and specimens show- 

 ing the external ornamentation. But the study of the collections under 

 consideration seems to anticipate at least two distinct species — the two 



