■VI 



cast or upon the enclosing matrix as in that one, and it is only 

 in the general form that the two approach each other. 



Dedicated to J. W. Foster, Esq. 



Geological Formation and Locality. In limestone of the age 

 of the Niagara group, near Chicago, III. Received from J. 

 W. Foster, Esq. ' 



CYRTOCERAS loculosum, (n. s.) 



Descriptian. Shell robust, somewhat rapidly increasing in 

 size and strongly curved, abruptly rounded on the dorsal and 

 ventral sides and much compressed laterally, becoming dis- 

 tinctly bilobate towards the outer chamber from the deep 

 rounded channel on each side, which is a little on the dorsal 

 side of the middle. 



In three specimens examined, the dorso-ventral diameter is 

 nearly or quite twice as great as the transverse diameter in 

 the outer portions of the shell, while on the older parts the 

 the diameters are more nearly equal, and the depressions upon 

 the sides scarcely marked. Septa moderately concave, numer- 

 ous, and sometimes very much crowded, strongly undulated 

 across the depressions on the sides; strongly arched forward 

 and produced on the back, the number ranging from sixteen to 

 twenty-four in the space of an inch upon the back, while on 

 the ventral side they are sometimes barely separated. 



Position of the siphuncle and surface characters of the shell 

 unknown. 



This species is quite distinct from any other known to me, 

 in the numerous crowded septa and the strong depressions 

 along the sides, which occur in three specimens in the same 

 relative position. The specimens are casts in magnesian lime- 

 stone, and no remains of the surface markings are preserved. 



Geological Formation and Locality. In limestone of the age 

 of the Trenton group of New York, at Madison, Wisconsin. 

 Collector. T. J. Hale. 



CYRTOCERAS orcas, (n. s.) 



Description. Shell robust, moderately curved, rapidly ex- 

 panding from the apex to the beginning of the outer chamber, 

 beyond which it is gently contracted towards the aperture. 

 One imperfect specimen of this species increases in its trans- 

 verse diameter from seven-eighths of an inch to one inch and 

 seven-eights in a length of two inches. The section is trans- 

 versely oval, the diameter being as ten to eleven and a half. 

 Septa moderately concave, distant, from five to six in a space 



