^8 BULLETIN OF THE LABORATORIES 



not greatly elevated beyond plane of hinge, the extremities of which 

 are met by the lateral oudine at about a right angle. Surface marked 

 by about twelve (8-12) sub-equal rather distant plicce and concentric, 

 irregular ridges, mesial sinus not so well defined and enlarged as usual. 

 Dorsal valve of the same general form, but somewhat less convex and 

 with less prominent beak; median fold, moderate and somewhat flat- 

 tened, with about five plicee on either side. 



This species is known from a single gathering, but a considerable 

 number of specimens of quite constant characters. It differs from the 

 preceding not only in greater size, but in the much less convexity and 

 projection of the beak and in the more transverse and square-shoul- 

 dered form. 



Height II mm ; length 17 mm. 



Small specimens have fewer plicce, but otherwise are similar. 

 From one mile north of " Dug-way," apparently below congl. II. 



Genus Terebratula. 



Subgenera Cryptonella and Centronella. 



The distinctions which separate the genera Cryptonella and Cen- 

 tronella from Terebratula are of such a character as can readily be re- 

 ferred to slight modifications of the structures characteristic of the last 

 named genus. It seems expedient, especially in view of the admitted 

 impossibility of distinguishing these groups without a knowledge of 

 the internal structures, to regard them as subgenera of the large and 

 characteristic genus Terebratula. 



Cryptonella eudora, H. 

 (Plate V, Fig. 10.) 



"Shell broadly ovate, rounded in front, apex obtuse. Ventral 

 valve gibbous in the central and upper part, moderately convex in the 

 lower part, and sometimes flattened toward the front ; tapering abrupt- 

 Iv to the beak, which is obtuse, little extended beyond the opposite 

 valve, slightly incurved, and truncated by a rounded foramen. Dor- 

 sal valve depressed-convex, often gibbous in the middle above; beak 



