I20 , Bulletin 31 120 



Claiborne sand since the day of Conrad, but its occurrence in 

 varietal forms are well-known in the St. Maurice beds below. 

 Even the Sabine has representatives. 



It is more globular in form than ozarkana and attains a 

 greater size, even 80 mm., or more in diameter. In certain 

 "Buhrstone" layers in southern Alabama this is the most abund- 

 ant and conspicuous fossil observed. However, on account of its 

 occurrence nearly always in the form of casts it has not been col- 

 lected and brought into museums as frequently as its importance 

 demands. 



Starting with a small, bullet-like variety {sylvcBrupis , n. 

 var. ) at Woods Bluff as seen considerably enlarged on pi. 39, 

 figs. 3 and 5, the dentition like [ozarkana seems here still further 

 weakened, yeX. there is a fairly sharp, compressed tooth in the 

 valve, under the beak ; in the right there is a remnant also of an 

 anterior lateral socket. The hinge line becomes very delicate, the 

 exterior marking is less regular and sharply defined than in 

 ozarkana but of the same general type. As the shell increases 

 in size in the St . Maurice beds it has the appearance shown by 

 &gs. 2 and 4 of pi. 39, loses all traces of dentition, shows but 

 rarely the fine Camptonedes sculpture, but sometimes larger 

 radii as indicated in fig. 4, shows quite generally an anterior an- 

 gulation, as also indicated in fig. 4, becomes very large and con- 

 spicuous, yet the shell substance is perhaps never much over .5 

 mm. in thickness. The shell when preserved seems to be of a 

 dull, porcellaneous composition, lustreless as the ordinary Lor- 

 ipes of today. 



It seems strange why this light, very abundant, prolific spe- 

 cies was not represented west of the Mississippi. 



It is impossible to state at present whether the form here 

 placed under this species, from pre-Claibornian horizons, was 

 really the ancestor of Conrad's subvexa of the Claiborne ; or 

 whether the Conradian species was derived from the ozarkaria 

 strain. The nomenclature of these forms is not definitely settled. 

 Dall regards ozarkana as simply the young of subvexa, but ad- 

 mits there is another larger species occurring in the St. Maurice 



