- 129 - ■ 



form from the Feocomian of the Paris Basin. Thus Sowerhj^'s name 

 is preoccupie"', althou?rh d'Qrbip-n^'s Iroa co.nso'brina is a Cucullae.?, 



In the coljections at hand cOuit adults of halidonata var^' 

 somewhat with re?rard to shape and the height of the umbones. Ihe 

 ty^^ical halidonata is relatively high and has high, prominent ura- 

 hones, hut there are variants in the direction of greater elonga- 

 tion and lower beahs. The end produe"^ of such variation is the 

 form describe"! by So^erby as Area consobrina« wiiich differs from 

 A. halidonata in being more elongated, in having a straighter 

 base line and lo'v7er and flatter umbones as Dall has shown. (1) 



(1). loe. cit. 



In addition, the -^mbones of Sowerijy's consobrina are plsced slight- 

 ly further toward the middle of the shell and the urjoer portion of 

 the posterior lateral margin is more oblique, in other words, the 

 angle betvreen the postero-dorsal aiid postero-lateral niar.~ins is 

 more obtuse. Since these differences are scarcely of specific 

 grade, and since, moreover, the end r)roducts are almost complete- 

 ly connected, it seems better to consider the more elongate form 

 as m.erely a variety of halidonata . In the collections at hand 

 there are only three large right v-.lves that can vath certainty 

 be referred to the variety, although, as state"^. above, some of the 

 halidonata forrris varj in that direction. The absence of any small- 



