135 ^1"- Maurice and Claiborne Pelecypoda 12- 



Ham's' original descriptio7i. — Size and general form as indicated by 

 the figure ; anterior somewhat produced, laterally compressed ; pofiterior 

 dorsal margin likewise somewhat compressed ; ventricose. 



This species is much more ventricose than inflata Lea, from the 

 Claiborne, and scarcely as much so as turgida Con. from the Vicksburg 

 beds. The umbones are intermediate in size between inflata and turgida, 

 the size greater than either. 



Dall combines turgida of the Vicksburg Oligocene beds with 

 bulla from the Jackson and anteprodnda from the St. Maurice 

 beds. Leaving aside the relationship of turgida and bulla for 

 future consideration, it may now be stated that the present wai- 

 ter, with the U. S. Museum material as used by Dall, plus large 

 collections from Texas and the Philadelphia Acadeni}^ material 

 under examination, saw^ a somewhat marked dissimilarity 

 between the Jackson btilla (fig. 9) and the St. Maurice antepro- 

 duda (figs. 6, 7, 8). The illustrations herewith given will as- 

 sist in showing such differences. Others might be given show- 

 ing a much wider range of variation. Our MS notes made at 

 the Academy (1892) with the Texas anteproduda and the Jack- 

 son (^/<//« in hand for comparison read : SphizreUa bulla Con., 

 from "Enterprise, Miss." [i.e. Jacksonian] consists of two 

 very imperfect fragments. The anterior part is evidently less 

 pointed than in the Texas Sphcerella. 



It has frequently seemed strange that these inflated Sphaerel- 

 las should be filled and sealed up so that the internal character- 

 istics are very difficult to determine. The interior is quite fre- 

 quently a cla}' iron-stone. Perhaps the mystery is solved to 

 some extent by the study of the dentition of a specimen found in 

 loose marl at St. Maurice. The dentition (see pi. 40, figs. 8 a, 

 b) consists — in the right valve — of an anterior cardinal, long, 

 sickle-shaped, curving well up into the beak of the opposite valve; 

 a posterior compound cardinal with one prong extending back- 

 wards at an angle of perhaps 45 degrees with the hinge margin 

 and with a second prong extensiveh' developed backwards into 

 an almost paddle-shaped extremity connected however below, 

 marginally by an extension, to the umbonal region of the shell. 

 This paddle-like portion of the tooth is twisted so that in viewing 



