ART. 3 MOLLUSKS FEOM UBUGUAY AND BRAZIL MARSHALL 6 



distant from the beak, the inner lateral being finely crenulated on 

 its upper surface. In this valve the two anterior laterals begin 

 near the beak, the inner one being finely crenulated on its upper 

 surface. Left valve with one anterior and one posterior lateral, 

 both crenulated on the edge. Anterior adductor scar deep; pos- 

 terior scar not so deep, but well marked. 



The type (Cat. No. 365382, U.S.N.M.) measures: Length, 27.5 

 mm.; height, 23 mm.; diameter, 14 mm. It comes from Arroyos 

 in the Department of Colonia, Uruguay, and was collected and pre- 

 sented by Prof. Auguste Teisseire. 



The finest specimen of all (Cat. No. 365380, U.S.N.M.) measuring: 

 Length, 28 mm.; height, 23 mm.; diameter, 15 mm.; has the teeth 

 abnormal and therefore could not be used as type. The abnormality 

 consists in having the two posterior cardinals of each valve fused 

 into a single tooth. The interior of this specimen is especially gay 

 with mixed colors of white, pink, lavender, and purple. Other 

 specimens which retain the true coloring of the interior show these 

 gay colors to be usual with the species. Younger and weathered 

 shells are greenish, or pinkish on the outside and show several radi- 

 ating fine lines. 



CORBICULA (CYANOCYCLAS) SIMPLEX, new species 



Plate 1, figs. 3, 4 



Shell rather thin, somewhat inflated, nearly round, but broader at 

 the rear than front, posteriorly subtruncate, anteriorly slightly ex- 

 tended. Dorsal margin well arched, beaks a little behind the middle, 

 anterior dorsal margin very oblique, posterior dorsal margin gently 

 sloping and shorter. Ventral margin regularly curved, rounding 

 gradually into the anterior margin and suddenly into the posterior 

 margin. Posterior ridge high but rounded; anterior ridge indis- 

 tinct; sculpture of fine concentric striae, more marked in front than 

 in the rear. Rest periods distinctly marked by deeper lines and 

 blackish color. Color olive green with a broad darker green ray on 

 the posterior ridge and two similar rays on the posterior dorsal area. 

 Interior purple with a white edging around the margin, the exterior 

 rays indicated by purple rays in the interior. In right valve the 

 anterior cardinal is minute and oblique, the middle cardinal thick 

 and deeply bifid, the posterior cardinal thick and moderately bifid 

 and oblique. In the left valve the anterior cardinal is moderately 

 thick, the middle cardinal is thick and deeply bifid, the posterior 

 cardinal long and thin. Right valve with two anterior and two 

 posterior laterals which are rather low and short, the inner ones 

 crenulated. Left valve with a single lateral in front and one at the 

 rear, both rather high and both crenulated. Adductor scars deeply 

 impressed, pallial sinus well marked. 



