AKT. 3 MOLLUSKS FROM URUGUAY AND BRAZIL MARSHALL O 



122321, U.S.N.M.) come from the Guahyba River, Rio Grande do 

 Sul, Brazil, and were presented by Dr. H. von Ihering. Almost any 

 one of the specimens might have been selected for the type as the 

 variation among them as to form, color, and sculpture is very slight, 

 while in size most of them approximate the type. 



This species is related to G. Imiosa but is distinguished at once by 

 the smaller size, the slightly more elongate form, and especially by 

 the very pale color. 



CORBICULA (CYANOCYCLAS) UNDULATA. new species 



Plate 1, figs. 5, 6 



Shell rather thick, subtriangular, inflated, obliquely truncated 

 posteriorly, rounded and slightly extended anteriorly, dorsal line 

 much arched, ventral margin evenly rounded, curving regularly into 

 the anterior margin, and more sharply into the posterior margin. 

 Posterior aspect wedge shaped, wide, and nearly at right angles 

 with the convexity of the shell. Beaks high and moderately nar- 

 row, pointing forward. Posterior ridge high and abrupt; anterior 

 ridge low and not well defined. Sculpture consisting of numerous 

 concentric ribs on the upper part of the shell which become less 

 marked near the ventral margin; on the posterior area there are 

 indications of obscure radiating ridges. Color dark yellowish 

 olive, with a number of green radiating lines which are not uniform 

 in width nor evenly spaced. Interior mainly dark purple, with 

 lighter area in the middle and along the margins. Each of the 

 radiating lines on the outer surface is marked by a dark purple 

 spot on the inner margin; pallial line and adductor scars well 

 marked, and the pallial sinus deep and wide. In each valve there 

 are three cardinal teeth, widely divergent. In right valve the an- 

 terior cardinal is thin and plateiike, the middle cardinal thick and 

 slightly bifid, the posterior cardinal medium thick and long and 

 bifid throughout its length. In left valve the anterior cardinal is 

 thick, the middle one like the one in the right valve, and the posterior 

 one thin. The right valve has two laterals anteriorly and two pos- 

 teriorly, rather short and stout and crenuiated. The left valve with 

 a short, thick, crenuiated lateral anteriorly and posteriorly. 



The type (Cat. No. 365392, U.S.N.M.,) measures: Length, 19 mm.; 

 height, 17 mm.; diameter, 13 mm. It comes from the Bay of 

 Colonia, Rio de la Plata, Uruguay, and was collected and presented 

 by Prof. Auguste Teisseire. 



This species differs from coloniensis chiefly in the strong concentric 

 ribs. Its proportions, too, are difl'erent, as it is more inflated. 



