1396 rossuLA 



Plagiodon balcani von Ihering, Arch, fiir Nat., 1893, p. 69, 



pi. ni, fig. 3. 

 Jheringella bahani Simpson, Syn., 1900, p. 914. 



This species is more triangular in outline than rottmdata, 

 the surface is rougher, the greatest degree of inflation is nearer 

 the posterior end. von Ihering states that the epidermis has 

 very fine, chain-like or twisted strije. 



Genus FOSSULA Lea, 1S70. 



Fossula Lf.a, Syn., 1870, p. 72 (footnote). 



Shell obovate, inflated, solid, with rather high beaks and a 

 low posterior ridge ; epidermis olive-brown, somewhat smooth, 

 sometimes slightly rayed ; there is an irregular tooth in the 

 left valve under the beak, and behind it a cavity ; in the right 

 valve there is a cavitv under the beak, and an irregular tooth 

 in front of and another behind it ; the teeth and cavities are 

 generally partly covered with brownish or amber-colored mat- 

 ter, and more or less pitted ; anterior cicatrices well marked, 

 united ; posterior faint ; prismatic border wide. 



Animal unknown. 



Type, Monocondylaa fossiculifera d'Orbigny. 



Conchologically the genera Monocondykca, Ihcr'mgella and 

 Fossula seem to be closely related. In the latter there is a 

 sort of ligamental matter in the cavities between the hinge 

 teeth that is often more or less regularly pitted. 



Fossui, A I'OSSTCU \A FiiRA ( d'Orbigny ) . 



. Shell obovate, short, subinflated or inflated, rather solid, in- 

 ecjuilateral ', beaks slightly elevated, not inflated ; posterior 

 ridge low. subangulate, sometimes appearing like a raised cord ; 

 dorsal outline lightly arched ; anterior end narrow, rounded ; 

 base well rounded to the end of the jiosterior ridge at or near 

 the median line ; dorsal slope obliquely truncate or subtrun- 

 cate ; surface with rude, irregular growth lines, sometimes with 

 traces of radial stria? ; epidermis olive to blackish, dull ; left 

 valve with an irregular tooth under the beak or a little in 

 front of it with a cavitv in front of and another behind the 



