4 PEOCEEDINGS OF THE NATIONAL MITSEUM. vol. 66 



CORBICULA (CYANOCYCLAS) COMPACTA, new species. 



Plate 2, figs. 10-12. 



Shell moderately inflated, thick, compact, siibrotund in outline, 

 narrower in front. Ventral margin slightly curved, anterior margin 

 narrowly curved, posterior margin sweepingly curved. Beaks rather 

 high and full, so placed as to give the shell an appearance of being 

 tilted forward. Posterior ridge prominent, obscurely subangular; 

 anterior ridge hardly apparent. Sculpture of rather distant but mod- 

 erately strong concentric growth striae, which are much stronger on 

 the anterior area. Periostracum clothlike, dull. Color light chestnut 

 brown, with several indistinct, hairlike darker vays. These rays are 

 on the calcareous portion of the shell, but • at places may be seen 

 through the translucent periostracum. Beaks eroded, allowing it to 

 be seen that the texture of the shell is of a pink color. Interior rose 

 pink, paler toward the margins. Cardinal teeth widely diverging. 

 In the right valve the first cardinal is reduced to a mere point, the 

 middle cardinal rather strong and bifid, the third about as strong as 

 the second and obscurely bifid. Anterior laterals of the valve rather 

 long, slightly bowed, the inner one the stronger and striated on its 

 upper face, the outer one weak. Posterior laterals of this valve very 

 short, the inner one stronger and weakly striated on its upper face, 

 the outer one very weak. In the left valve the first cardinal tooth is 

 thin and platelike, the second is stronger and obscurely bifid, the 

 third is an elevated, thin plate. Tlie anterior lateral tooth of this 

 valve is bowed and irregularly crenulated and striated. The poste- 

 rior lateral is extremely short and weakly striated. Adductor scars 

 and pallial line impressed, the pallial sinus very marked. 



The type. Cat. No. 349175, U.S.N.M., measures: Length, 25 nmi.; 

 height, 22.5 mm. ; diameter, 17.5 mm. It comes from Doctor Felip- 

 pone, who collected it at Paysandu, Uruguay. 



The chunky form, compactness, pinkish color, and especially the 

 very small posterior lateral teeth afford easy means of identifying 

 this species. 



CORBICULA (CYANOCYCLAS) DELICATA, new species. 



Plate 2, figs. 4-6. 



Shell moderately compressed, subquadrate in outline, wide poste- 

 riorly, where it is roundly truncate. Anterior end shortly rounded, 

 ventral margin slightly rounded, hinge line very lightly arched, beaks 

 a little behind the middle. Posterior ridge moderately high, rounded, 

 posterior dorsal area sloping gently from the ridge to the margin, 

 wide. Sculpture of very fine concentric striae, the rest periods indi- 

 cated by a deeper line and of dark color. Periostracum clothlike, not 



