﻿36 I.AMPSII.IS 



erally smooth and shining, often briUiantly rayed ; beak sculp- 

 ture, for the most part, consisting of tine, parallel ridges, which 

 show a tendency to fall into an anterior and posterior loop ; 

 hinge with one or two pseudocardinals and one lateral in the 

 right valve, and two pseudocardinals and two laterals in the 

 left ; female shell having a moderate and gradual inflation in 

 the post-ventral region opposite the marsupium. Animal hav- 

 ing the inner gills usually attached nearly or quite their entire 

 length to the abdominal sack ; marsupium occupying the hinder 

 part of the outer gills ; ovisacs distinct, separated by sulci, 

 rounded below having a fold near their bases, the whole pro- 

 jecting below the inner gills ; mantle edge double and thick- 

 ened, often swollen behind into a sort of flap in the female. 



Type : Unio ovatus Say. 



The genus Lampsilis contains a large number of North 

 American Uniones of a high type, usually having decidedly 

 dimorphic shells. The marsupium is placed in the hinder part 

 of the outer gills and consists of few to many distinctly mark- 

 ed ovisacs, the whole of somewhat dififerent appearance from 

 the rest of the gill, even when empty. The genus apparently 

 does not rank so high as does TruncUla, as there is not such 

 a remarkable difference between the shells of the sexes. In 

 the female shells of the latter group the marsupial area is gen- 

 erally (fnite distinctly marked off from the rest of the shell, 

 being thinner, of different texture, often suddenly inflated and 

 radially ridged and toothed. In Lampsilis this area consists 

 of a mere gradual inflation, sometimes quite feeble or hardly 

 perceptible; it is rarely much thinner than the surrounding 

 shell and never toothed or striated or of different texture. 



The genus seems to be naturally divisible into four groups: 

 Lampsilis typical, Eiirynia, CarHncnlina and Proptcra. I can- 

 not be certain what Rafinesque's Lampsilis cardinni is, but it 

 is doubtless a member of the group to which Unio ventricosus, 

 capax and cariosus belong. These species are characterized by 

 inflated, large shells, the male and female being dimurphic, and 

 having coarsely sculptured beaks. Eitrynia contains the forms 



