4 PROCEEDINGS OF THE JSTATIOISrAL MUSEUM vol. 72 



The type (Cat. No. 3G5385, U.S.N.M.) measures: Length, 24.5 

 mm.; height, 21.5 mm.; diameter, 18.5 mm. It and a single valve 

 (Cat. No. 365386, U.S.N.M.) come from Arroyos in the Department oi 

 Colonia, Uruguay, and were collected and presented by Prof. Auguste 

 Teisseire. 



This species is closely related to G . teisseirH^ but differs in the 

 shortened posterior end and in the greenish color. 



Two specimens (Cat. Nos. 365387 and 365388) from Arroyos in 

 the Department of Colonia, Uruguay, sent by Professor Teisseire, 

 contain young in the dried flesh of the mother. The largest of these 

 young is 4I/2 mm. long. The parent shell has a length of 211/0 ^xvai. 

 In the young the tips of the beaks are glassy, tinged with lavender, 

 followed by a broad splash of white, which is surrounded by an 

 irregular circle of violet, then a whitish, concentric band and the 

 ventral portion purplish. The posterior area shows three purple 

 rays. These are the beginnings of the three external fuscous rays 

 .and internal purple rays of the adult. 



CORBICULA (CYANOCYCLAS) GUAHYBENSIS, new species 



Plate 1, figs. 9, 10 ^ 



Shell small, rather compressed, nearly elliptic, slightly narrower in 

 front than behind. Dorsal margin regularly curved, beaks a little in 

 front of the middle, anterior dorsal margin slightly more oblique 

 than the posterior. Ventral margin lightly curved, rounding grad- 

 ually into the anterior margin and somewhat more sharply into the 

 posterior. Anterior and posterior ridges rounded, not well defined. 

 Sculpture of numerous fine concentric striae, stronger on the an- 

 terior and posterior areas; the rest periods emphasized. Most of 

 the shell glossy, very light straw color, becoming darker with dis- 

 tance from the beaks. Surface with a number of narrow, unequal 

 reddish rays, three of which are more prominent than the others. 

 Interior mostly white with a large spot of lavender in the upper part. 

 In right valve the anterior and posterior cardinals are oblique and 

 thin, the latter larger than the former, the middle tooth thick and 

 slightly bifid on its summit. In left valve the anterior cardinal is 

 thicker and shorter than the posterior; the middle tooth thick and 

 distinctly bifid. In right valve the two pairs of laterals are short 

 and stout, the groove between each pair wide and deep, and the inner 

 ones finely and sharply crenulated. In left valve there is one ante- 

 rior and one jDOsterior lateral, both of which are rather thick and 

 finely crenulated. Adductor scars deep ; the sinus in the pallial line 

 wide, obtusely pointed, and unusually well marked. 



The type (Cat. No. 171426, U.S.N.M.) measures: Length, 15 mm.; 

 height, 13 mm.; diameter, 8i/^ mm. It and 28 paratypes (Cat, No. 



