324 THE PEARLY FRESR-WATEK MUSSELS— SIMPSON. vol. xviii. 



labial x)alpi, which are attached in a curved line above, and which are 

 not united posteriorly. Otherwise the animal does not seem to differ 

 greatly from that of TJnio. 



Genus FOSSULA, Lea.' 



In 1870, Lea separated Monocondylcea fossieulifera, d'Orbigny, from 

 the genus in which it had been formerly placed, and gave it the above 

 generic name. The shell is solid, and externally quite closely resembles 

 that of Glabaris lato-marginatH, Lea, but tlie hinge is peculiar. In that 

 of the left valve there are two distinct humps, with a depression between, 

 which latter is opposite the beak. In the right there is a large, blunt 

 elevation which fits into this depression of the left valve; then behind 

 this is a pit, and still behind it a smaller hump. Frequently a smaller 

 set of denticles are seen above one or more of the pits, which project 

 into a sort of ligament in the up])er part of the hinge. This latter 

 character is shown more i)laiuly in a species recently named F. hulzani 

 by V. Ihering. The animal is said by this author to scarcely differ 

 from that of Glabaris ^^ 



Genus IHERINGELLA, Pilsbry.' 



In 1859, Lea applied the name Flag iodon* to Monocondylcea isocardi- 

 oides, Lea, but as that name liad been i)reoccupied by Dumeril in rep- 

 tilia(1835), Pilsbry proi)osed the mime I he ring elJ a for it, in honor of the 

 eminent biologist von Ihering, who has done such excellent work among 

 the iSTaiades. The type, P. isocardioides, Lea, resembles in form an 

 Isocardw. The hinge appears as if injured, like that of uMargaritana. 

 In the right valve are two irregular teeth under the beak, and a broken, 

 saddle-shaped tooth in the left valve fits in between them. In each 

 valve there are pseudolaterals which start under the beak and slope 

 downward across the plate, and the whole surface of the hinge is cov- 

 ered — teeth and all — with irregular wrinkles and pustules. Concho- 

 logically it seems most closely related to Monocondijliva. The nacre has 

 a peculiarly soft, greenish hue. The animal is unknown. 



Genus MYCETOPODA, d'Orbigny.-' 



Orbigny first applied the above name to M. Soleniformis, Orbigny, 

 and M. Siliquosus, Orbigny, characterizing the genus in a proper man- 

 ner, and afterwards, in the "Voyage Amerique Meridionale," changed 

 the name without explanation to Mgcetopus^ by which it is generally 

 known. The former name wdl, 1 am sorry to say, have to supersede 

 the latter. 



' Synopsis of the UnionidiB, p. 72, 1870. 

 ^Archiv fiir Naturgeschichte, I, pt. 1, p. 65, 1893. 

 sKautilus, VII, No. 3, p. 30, 1893. 

 "Proc. Acad. Nat. Sci. Phila., VIII, p. 79. 

 Hiuer. Mag. Zool. CI., V, No. 62, p. 41, 1835. 



