SCAMMON : THE UNIONID.E OF KANSAS, PART I. 341 



TETRAGENE.E. 



"Male and female shells alike, solid; beak sculpture con- 

 sisting of coarse subparallel ridges ; beak cavities deep ; mar- 

 supium rilling all four gills, smooth, pad-like." (Simpson.) 



Genus QUADRULA (Rafinesque, 1820) Agassiz. 



"Shell triangular quadrate or rhomboid, solid, inflated, 

 with rather prominent beaks, which are generally sculptured 

 with a few coarse, irregular, subparallel ridges that are in- 

 flated when they cross the posterior ridge ; posterior ridge 

 ordinarily well developed ; base often incurved in old speci- 

 mens ; disks sculptured or smooth ; epidermis usually dull 

 colored, dark, and rayless or feebly rayed; hinge plate 

 heavy, wide, flattened ; pseudocardinals solid, direct, ragged ; 

 laterals double in the left and single in the right valve, often 

 with a secondary lateral below the large one in the right 

 valve ; cavity of the beaks deep and compressed ; dorsal 

 scars under the hinge plate ; male and female shells alike. 



"Animal having the inner gills the larger, generally free 

 from the abdominal sac the greater part or all of their 

 length ; marsupium occupying all the four gills throughout, 

 the whole smooth and pad-like." (Simpson.) 



Quadrula plicata Say. Plate LXXIX. 



Unio plicata Say, Nich. Encyc, II, 1816, pi. in, fig. 1. 



Shell large, thick, particularly anteriorly, wide, oval in 

 outline. Anterior margin flatly curved ; ventral margin gently 

 bowed ; posterior margin bluntly rounded or roundly biangu- 

 late ; dorsal margin straight or slightly curved and slightly 

 oblique. Umbones large, inflated, high, directed anteriorly, 

 sculptured at the tips with several coarse ridges. Umboidal 

 ratio, from 0.07 to 0.14. The disk of the shell covered with 

 from four to nine coarse, parallel, more or less irregular folds, 

 which extend obliquely from the highest portion of the beaks 

 to the ventral and posterior margins. Anterior slope short, 

 abrubtly curved ; posterior slope somewhat abrupt, slightly 

 excavated, sometimes marked with a series of short plications 



5-Bull.. Vol. Ill, No. 9. 



