AIM'.- 15 MOLLUSKS OF THE GENUS COEBICULA MARSHALL, 9 



valve veiy thick, especially at the base. Color of interior various 

 shades of purple and ash-gray, the latter color forming a narrow 

 band around the margin, and inside of this are two irregular zones 

 of purple with ash-gray between them. Adductor scars purple and 

 a spot of the same color at the upper end of the lateral teeth of each 

 valve. Cavity of the shell lavender. Adductor scars and sinus of 

 the pallial line deeply impressed. 



The type, Cat. No. 109261, U.S.N.M., measures: length, 7.5 mm.; 

 height, mm.; diameter, 9 mm. It and an additional left valve 

 come from Arroyo de Malvin, Department of Montevideo, Uruguay, 

 and were presented by Mr. S. Olea, in whose honor the species is 

 named. It was in specimens of Co'rhicida presented by Mr. Olea 

 tliat Doctor Dall made the first discovery of viviparity in this genus. 



Cat. Xo. 334554, U.S.N.M., contains a left valve of this species 

 from the Uruguay River, Paj-sandu, Uruguay, from Doctor Felip- 

 pone. 



The obliquity, the strength, the very cordate form, and especially 

 the concentric ridges on the upper half of each valve make this 

 species easy of identification. 



CORBICULA (CYANOCYCLAS) PAYSANDUENSIS. new species. 



Plate 1, Figs. 5, 6, 8. 



Shell inflated, subquadrate in outline, shortly rounded anteriorly, 

 nearly squarely truncated posteriorly, beaks a little back of the mid- 

 dle, posterior ridge high, subangular, anterior end' of shell pouting 

 forward. Periostracum not gloss3% smooth, unctuous. Sculpture 

 consisting of a number of elevated concentric ridges near the beaks 

 and similar concentric ridges on most of the anterior area which die 

 nut before reacliing the main convexity of the shell. There are 

 numerous Aveak growth striae, but the principal rest periods are well 

 marked by a stronger line and a band of darker color. Posterior 

 area with indications of several weak radiating raised lines. Coloi- 

 dark olive green, with indications of several narrow radiating, chest- 

 nut-colored lines. Color of interior purplisli gray, the radiating 

 chestnut lines of the exterior showing between the pallial line and 

 the margin. Cardinal teeth moderately diverging. In the right 

 valve the first cardinal is small and pointed, the second is strong and 

 bifid, the third not quite so strong but more deeplj^ bifid. In the left 

 valve the first cardinal is high and pointed, the second bifid on its 

 ventral face, the third long and with a raised point at its lower end. 

 Anterior laterals of right valve nearly straight, subequal in strength, 

 tlie inner one sharply crenulate. Posterior laterals in this valve 

 remote from beaks, short, much bowed, the inner one crenulate. In 

 tlie left valve the anterior lateral is thin, crenulated: posterior one 



