Ortmann: Families \m> Genera of Najades. :;'-!l 



marsupium in this genus is not very peculiar, though assuming the 

 characteristic kidney-shape of the higher Lampsilince. The tusk of 

 aerating the glochidia is taken up by the edge of the mantle in front 

 of the branchial opening. However, the latter is as yet very little 

 differentiated morphologically, bu1 the thickened (muscular) margin 

 and the pigment indicate that it actually lias a special function. The 

 shell of Obovaria presents no remarkable features, though it is possibly 

 archaic, for it reminds of certain forms of Fusconaja and Quadrula. 



This genus is divided by Simpson into two subgenera, which are 

 very well defined. 



Subgenus Obovaria (sens, strict.). 



Shell rounded, rather upright, beaks more or less in the middle of the 

 upper margin. Pseudocardinals normal and divergent. 



Type 0. retusa (Lamarck). 



Subgenus Pseudoon Simpson (19006, p. 601). 



Shell ovate, oblique, beaks finite anterior. Pseudocardinals (at 

 least in old shells) oblique, almost parallel to the laterals. 



Type 0. ellipsis (Lea). 



At first glance, 0. ellipsis looks very different from typical Obovaria. 

 and I was for some time inclined to unite it with Nephronajas; but 

 O. castanca clearly forms a connection with the typical forms. 



Simpson (/. c.) describes the soft parts of Pseudoon, and says: 

 " mantle having a wide, thickened, double border, the inner edge being 

 toothed throughout below." This is incorrect. The inner edge is 

 slightly widened and crenulated only for a short distance in front of 

 the branchial. Simpson also says that the ovisacs are "tinted with 

 purple below." I have not seen this in 0. castanea, although 0. 

 ellipsis has a slight purplish gray pigment at the edge of the marsupium ; 

 but this should not be described as "purple." 



Obovaria retusa (Lamarck). 



On August 29, 1908, I found a gravid female with eggs in the Ohio 

 River in Beaver Co., Pennsylvania, and on September 22, 1910, I 

 secured two males and two gravid females, with glochidia, in the 

 Ohio River at Portland, Meigs Co., Ohio. 



The soft parts have been described by Lea (Obs., X, 1863, p. 433). 



Anal and supra-anal separated by a short mantle-connection. Anal 

 crenulated, branchial with papilla?. In front of the branchial the inner 

 edge of the mantle in the female is slightly dilated and lamelliform, 



