9 



From the foregoing description it will be seen that this 

 species is closely related to the Terebratula Royssii of Leveille, 

 and to T. planosulcata of Phillips. It differs from the first in 

 its small size and more ovate form, especially of young in- 

 dividuals, and in' never having the distinct sinus possessed 

 by that shell ; while the beaks of our shell are more promi- 

 nent and the slope on each side is less concave. The volu- 

 tions of the internal spire in T. hirsuta are not more than 

 half the number represented in T. Royssii. From the T. pla- 

 nosulcata it differs in its smaller size, in being less ventricose, 

 especially towards the front margin, in the proportionally 

 more prominent beaks and generally more elongate form. 

 From the specimens examined the projecting spinose lamel- 

 lae in our shell are never so much extended as in that species. 



RETZIA, King. 



* Retzia Verneuilana. — Shell longitudinally ovate ; valves 

 almost equally convex ; dorsal (ventral) valve most promi- 

 nent near the beak, which is elevated and incurved so as to 

 bring the circular foramen nearly on a line with the mar- 

 gins of the valves ; foramen round ; ventral valve smaller, 

 auriculated on the cardinal angles, beak small, scarcely 

 rising above the straight cardinal margin ; area small, tri- 

 angular, not entirely confined to the larger valve, bounded 

 by a distinct angular margin. Surface longitudinally striate, 

 marked by about fifty rounded, beautifully punctate, simple 

 strise. 



Length, *10 to '32, width '08 to '27 of an inch, usually. 

 Some specimens have a length of three-fourths of an inch. 

 Locality. — Spergen Hill ; Bloomington, la. 



RHYNCONELLA, Fischer. 



' Rhynconella ricinula. — Shell very small, longitudinally 

 ovate or sublenticular, neatly rounded in front ; valves 

 almost equally convex ; beak of dorsal (ventral) valve 

 straight, comparatively much extended, perforate by a tri- 

 [Trans. iv.] 3 



