PALEONTOLOGY. 413 



Genus NUCLEOSPIRA Hall. 

 Nuclcospira rotiindata. 

 Plate I, figs. 11-14. 

 Nucleospira rotundata Whitf., Ann. N. Y. Acad. Sci., 1882, p. 194. 



Shell attaining a rather large size for the genus, being often more than ha 1 f an 

 inch in transverse diameter, and when of medium or large size, strongly ventricose 

 or rotund. The younger individuals, however, are depressed-convex or lenticular 

 in profile. Length of the shell as great or greater than the transverse diameter. 

 Beaks small and incurved, not at all conspicuous. Valves marked by a slight de- 

 pression along the median line, strongest on the ventral side. 



This species, like all those of this formation yet obtained in Ohio > 

 are mostly" internal casts and impressions; consequently the true features 

 of the shell are not readily obtained. The general features of the 

 species, however, are preserved sufficiently for identification and com- 

 parison, when good individuals are selected. The shell bears much re- 

 semblance to N. ventricosa, Con., from the Lower Helderberg group of 

 New York, in its general form, except the much greater size and more 

 elongated form of the adult individuals. There is more difficulty in 

 separating them satisfactorily from the casts of Meristclla bella Hall, 

 with which they are associated. In fact, it is all but impossible to do 

 this with certainty, unless they are in a good state of preservation, as 

 the difference in the form of the muscular imprint of the ventral valve, 

 and the more strongly incurved beaks, are the only features that can be 

 relied upon. 



Formation and Locality. — In the hydraulic limestone of the Lower 

 Helderberg group, at Greenfield, Ohio. 



Genus RETZIA King. 



Retzia formosa. 



Plate I, figs. 15 and 16. 

 Waldheimia formosa Hall, 10th Rep. State Cab., 1857, p. 88. 

 Trematospira formosa Hall, Pal. N. Y., vol. 3, p. 215, pi. 36, fig. 2. 

 Rhynchospira formosa Hall, Pal. N. Y., vol. 3, p. 485, pi. 95 A, figs. 7-11. 



Shell small, the specimens observed not exceeding five-sixteenths of an inch 

 in length, by about one-fourth of an inch or less in width; elongate-ovate in form, 

 widest below the middle and narrowing at the beak on the ventral side, the apex 

 being slightly incurved. Valves highly convex, with a slight depression along the 

 middle. Surface of the shell marked by about twenty-two simple, round, radiating 

 plications, two of which in the middle of the valves are more slender than the 

 others and depressed below their level, forming a slight mesial sinus on each valve. 



The shell, or rather the impression of the shell of this species as left 

 in the rock, appears to represent an adult specimen, but is very much 

 smaller than those of the Lower Helderberg group of New York, or 

 those of R. evax in the Niagara group at Waldron, Indiana, but possesses 

 all the essential specific characters of the species except in this one 



