1913.] 



NATURAL SCIENCES OF PHILADELPHIA. 



499 



Diplodonta mediamericana n. sp. Fig. 2. 



The shell is of the usual orbicular shape, the length and altitude 

 about equal, diameter nearly two-thirds of the length; rather thin; 

 surface densely and very delicately striate, smoother towards the 

 beaks, which are somewhat prominent. 

 Margins somewhat straightened on both 

 sides of the beaks; the anterior end a little 

 more broadly rounded than the posterior. 

 Teeth rather strong. Length 15.5, alt. 15.1, 

 diam. 9.8 mm. 



Porto Barrios and Livingston, Guatemala,, 

 in mud brought up on an anchor, S. L. 

 Schumo, cotypes No. 76,479 A. N. S. P. 

 Fig. 2. -~ Diplodonta medi- ^^^^^ ^j^_ jj^pg Professor W. B. Scott. 

 amencuna n. sp. . , , i i tn 



This species closely resembles D. puiic- 



turella Dall, but differs in the sculpture and proportions. D. nuclei- 

 formis (Wagner) is a much smaller and more obese form. 

 Leda vulgaris n. sp. Fig. .3. 



The shell is rather solid, plump, equivalve; beaks median, small, 

 contiguous. Anterior end rounded, its upper margin convex. Pos- 

 terior end rapidly tapering, attenuate, 

 its upper margin concave. Surface 

 glossy, with fine, regular sculpture of 

 concentric grooves as wide as the in- 

 tervening ridges. The posterior dor- 

 sal surface is flattened, striate, bounded 

 by strong ridges, giving the appearance 

 of a large, lanceolate escutcheon. 

 There are 16 anterior and about 26 

 posterior teeth. 



Length 12, alt. 6.3, diam. 5.2 mm. 

 Length 11.5, alt. 6.3, diam, 6 mm. 

 This species, which is extremely 

 abundant in the Mount Hope For- 

 mation, was also obtained in mud from an anchor collected by 

 Mr. S. L. Schumo at Porto Barrios, Livingston, Belize, and INIonkey 

 River, and is therefore a common form of the Central American 

 litoral. L, commutata Phil., which seems closely related, is a wider 

 species, the basal margin being more deeply arcuate. L. mauritiana 

 Sowerby is very similar, but in various details is nearer to L. jamai- 

 censis Orb. 



Fig. 3. — Leda vulgaris n. sp. 



