139^ Fossur.A 



The form of this does not differ greatly from some of Lea's 

 specimens of fossiculifera, but the regular crenation in the 

 middle of the hinge line, if constant, ought to be a good dis- 

 tinguishing character. 



FossuLA BKAZiLiENSis von Ihering. 



"'J'his species is considerably smaller than F. fossiciilifera 

 and is distinguished from it by the smaller anterior end and 

 the much more inflated posterior half of the shell. The beaks 

 are smaller and less prominent than in that species. In the 

 example from the Paraguassu River, which is 42 mm. long, 

 T,T, mm. high and 22 mm. in diameter, they are situated at 13 

 mm. from the anterior end. The length of the hinge to 

 the beginning of the sinulus is 26 mm. and the distance 

 of the beaks from its anterior end is 8 mm. The dorsal 

 margin is obliquely inclined from behind and above to 

 the front and is slightly convex posteriorly. Posterior mar- 

 gin oblique above and convex below, fonning a blunt angle 

 at about the centre. The anterior margin is regularly rounded. 

 Ventral margin oblique and nearly straight in front, convex 

 behind. The greatest height is at 13 mm. from the posterior 

 end. Surface smooth, with close, thread-like growth lines, 

 which towards the ventral margin become irregular, thicker 

 and further apart. Somewhat in front of the centre is a 

 broad, flat impression, which extends from the beaks to the 

 ventral margin. Behind this impression the shell is remark- 

 ably inflated. From the beaks to the angle in the posterior 

 margin is a strong elevated line, which borders the somewhat 

 concave dorsal area. The lunule is very small, quite indistinct. 

 At the anterior end of the hinge are three downward pointed 

 continuations of the ligament, through which the tooth-like 

 thickenings of the hinge, which are lacking in the right valve, 

 are shown. The rather thick hinge of the right valve has a 

 long, subobsolete, forvvardly curved tooth, which fits into a lig- 

 ament covered cavity in the left valve, 7 mm. long. On the 

 closed shell, which gapes only a little in front and behind, the 

 beaks are 2 mm. from each other and the part of the shell 



