150 Bulletin 31 150 



46, fig. 8) seems to be an intermediate form. 



'Caryatis exigua" Conrad, PI. 47. Fig- 7 



Caryaiis exigua Con., Amer. Jour. Conch., vol. 6, 1871, p. 201, pi. 11, 



fig- 3- 



Conrad's original description. — Subcordate, short and elevated, 

 ventricose, thin in substance ; summits prominent ; posterior side truncated; 

 lunule cordate ; indistinctly defined, Claiborne. Rare. 



We are quite at a loss to know what Conrad had in hand 

 while describing and figuring this so-called species. We have 

 not been able to find the t3^pe in the Academy's collections and 

 presinne it is lost. 



Meretrix yoakumi Gabb, 



".^ Meretrix yoakmnV' Gabb, Proc. Acad. Nat. Sci. , Phila. 1861, p. 

 370. 



Gabb's origiftal description. — Shell subquadrate ; beaks prominent, 

 placed one-third of the distance from the anterior extremity, which is reg- 

 ularly rounded, posterior cardinal margin straight. Anal extremity sub- 

 truncated. Surface marked by numerous very regular concentric ribs, 

 which are abrupt on the side towards the beak, and slope concavely on the 

 other side. Crests of the ribs rounded or subangular. Interspaces a little 

 wider than the ribs. 



Length, .3 in. ; width, .4 ; height of valve, .09 in. 



From a brown, highly ferruginous sandstone (Eocene), Caddo Peak, 

 Texas. Collected b}^ Prof. Yoakum. 



The specimen being so imbedded that I could not obtain a view of the 

 hinge, renders the determination of the genus somewhat doubtful ; but 

 since it presents the usual appearance of this genus more strongly than of 

 any other, I refer the species provisionally as above. The shallow valve, 

 the abrupt posterior end, and the very distinct ribs f about thirty in number 

 on the specimen before me), will serve to separate the species from all the 

 other known species. 



The t3^pe of this species does not seem to be in the collection 

 of the Academy of Natural Sciences of Philadelphia and hence it 

 is doubtless lost. The general form is apparently like that of 

 bastropensis, but the number of ribs is obviousl)^ far less. The 

 peculiarities in the shape of the ribs are not observable in bastrop- 

 eiisis. Gabb, moreover, was not sure of the generic position of 

 his specimen ; it was small, imperfect and unique. Under such 



