UNIOOTD^ FEOM THE CAMDEN CLAYS. 249 



separating them as species. Mr. Lea remarks of this species that its form is 

 very unusual, and that it is aUied to U, Boanokoensis and U. macer Lea ; also, 

 that it is remarkably compressed at the anterior end for a Unio, but that the 

 same character applies to others from the same locality. 



Uuio ligamentiuoides. 



Plate XXXII, Fig. 4, and Plate XXXIV, Fig. 8. 



Unto ligamentinoides Lea. Proc. A. 1^, Sci., Phil., 1868, p. 164. Pamphlet by Lea, p. 31. 



Shell longitudinally ovate and somewhat regular in outline ; rather 

 broader behind than in front. Hinge-line rather strongly arcuate, more 

 strongly bent just in front of the beaks, which are situated nearly at the 

 anterior third of the length of the shell. Basal margin strongly and regu- 

 larly curved. Valves compressed. Lateral teeth comparatively slender and 

 curved ; cardinal tooth large and only moderately thick. Anterior mus- 

 cular scar comparatively large, moderately deep. Posterior scar very faintly 

 marked. 



The shell has very much the outline of the male of U. ligamentinus Lea, 

 and is readily distinguished from specimens of U, radiatoides by its rounder 

 form. The type specimen of Dr. Lea is more pointed posteriorly than others 

 which I have seen, and the valves rather more compressed. Besides, it has 

 some appearance of a slight alation at the posterior extremity of the car- 

 dinal line, and might readily be taken for a vertically compressed individual 

 of U. alatoides. The epidermis is also less rugose than in some of the others. 



Unio alatoides. 

 Plate XXXIII, Figs. 3 and 4, and Plate XXXIV, Fig. 6. 

 Unio alatoides Lea. Proc. A. N. Sci., Phil., 1868, p. 164. Pamphlet by Lea, p. 32. 



Shell compressed, broadly ovate, very much wider posteriorly than in 

 front, the posterior alation giving a broader form and a more direct upward 

 tendency to the lines of growth, even when the alation itself is not pre- 

 served. Umbones very much compressed and the beaks hardly perceptibly 

 elevated. The teeth are not visible in either of the two specimens before 

 me nor are the muscular scars sufficiently well marked to warrant a de- 



