UNIONID^ FEOM THE CAMDEN CLAYS. 251 



treraely narrow approaching pointed and longest above the middle of the 

 height; posterior end broader and obtusely rounded and longest below. 

 Valves compressed, more convex behind than in front where they have been 

 quite attenuate ; anterior muscular scar quite moderate in size, but well . 

 marked; posterior scar faint. Cardinal teeth strong, apparently double. 

 Lateral teeth apparently straight and moderately strong. Surface of the 

 shell not observed. 



This species presents strongly the features of U. rectus, from the Ohio 

 watershed, but perhaps even more strongly those of the species from the 

 waters of Georgia and Alabama. It is so very distinct in its elongate nar- 

 row form from any of those associated witli it that it cannot well be mis- 

 taken. 



Geuus ANODONTA Cuvier. 



Auodouta grandoides. 



Plate XXXV, Figs. 2 and 3. 



Anodonta grandoides Lea. Proc. A. N. S., Phil., 1868, p. 164. Pamphlet, 1868, p. 32. 



Mr. Lea's description of this species reads as follows: "Shell smooth, 

 elliptical, very much inflated, ventricose, obtusely angular behind, obliquely 

 rounded before ; beaks submedial, flattened on the tips, but very much in- 

 flated on the umbos." 



The shells of this species in the collection under consideration are much 

 better preserved than those of A. corpulentoides, probably because they were 

 somewhat stronger, and perhaps also because from their somewhat greater 

 length they were less liable to become imbedded obliquely in the sediment, 

 and thus escaped the oblique pressure to which many of the others were 

 subjected. Their form appears to have been less inflated than A. corjntlen- 

 toides, with the beaks less central, the posterior end being longer proportion- 

 ally, as well as much more pointed, and more angular along the posterior 

 umboual ridge, while the proportional height of the shell is considerably less. 

 One of the specimens on which these observations are based retains nearly 

 its original form, being only slightly compressed and having much of the 

 epidermal layer preserved. There are several other shells among our fresh- 

 water forms that bear considerable resemblance to this one, as well as A. 



