INVERTEBRATE PALAEONTOLOGY. 133 



name for the divaricate section, for which I also use it here, but I adopt il as 

 II. and A. Adams' name, not Klein's. 



The next name applied lo any type of this genus was Lucina, Lamarck, 

 1801. Nearly all authors have- adopted the latter name for the genus, while 

 several use Scopoli's name Codakia subgenerically under it. Ifthistypeis 

 to be admitted into the genus at all, however, it seems to me that Codakia, 

 being the oldest regularly-proposed name for the genus, would have to be 

 adopted for it, and the costate species, with the other characters mentioned, 

 viewed as the typical section ; for I cannot see how a genus once regularly 

 proposed, can be reduced to the rank of a subgenus under another published 

 at a later date, even though the first name may not have been adopted in the 

 interval. Such a rule would give any author who might find a type differing 

 only subgenerically from any recently-published genus, the right to reduce the 

 same to the rank of a subgenus, and give a new generic name for the whole 

 group himself; a course that has, in fact, actually been pursued in one or 

 two instances by Dr. Stoliczka. 



Lucina s u b u n d a t a , H. & M. 



Plato 17, fig. 2, a, b, e, <?, e. 

 Lucina sitbiuidala, Hall and Meek (1854), Mora. Am. Acad. Arts and Sci. Boston, V (n. s.), pi. i, fig. 6. 



Shell small, subcircular, compressed, very thin ; anterior side broadly 

 rounded; basal margin semi-ovate, the most prominent part being toward the 

 front, more or less contracted behind, smooth within ; posterior side narrower 

 than the other, and usually subtruncate at the extremity; dorsal margin 

 concave in outline, just before, and convex just behind the beaks, which 

 are rather prominent, pointed, and nearly central. Surface ornamented by 

 small concentric undulations, and very small parallel striae, which are some- 

 times crossed by obscure traces of very fine, nearly obsolete, radiating stria;. 



Length, 0.42 inch ; height, 0.32 inch ; convexity, 0.12 inch. 



This little shell evidently' varies much in form, some specimens having 

 the anterior portion of the ventral margin much more prominent, and the 

 posterior side more contracted, than others. Generally, there is an obscure 

 depression extending obliquely backward and downward from the posterior 

 side of the beaks, and a stronger one passing from the front side of the beaks 

 to the upper part of the anterior margin. Sometimes both of these 



