A3T. 17 SHELLS FROM BRAZIL AND URUGUAY MARSHALL 5 



margin. Dorsal line nearly straight, fading without an angl<^ into 

 the posterior margin, which in turn sharply rounds into the ventral 

 margin. Ventral margin very lightly curved, sloping up to and grad- 

 ually rounding into the anterior margin. Beaks set back about 20 

 mm. from the extreme anterior margin and 75 mm. in front of the 

 extreme posterior point. Posterior ridge somewhat angular, but low, 

 with the descent to the margins gradual. Anterior ridge rounded, 

 set close to the anterior margin. Sculpture of poorly marked con- 

 centric lines of growth and obscure radiating striae, with indications 

 of a few radiating ruffles. Color nearly uniform light chestnut. 

 Interior rich pink lavender. 



The type (Cat. No. 368235, U.S.N.M.) measures: Length, 95 mm.; 

 height, 38 mm.; diameter, 20 mm. It comes from Canada Grande, 

 Department of Cerro Largo, Uruguay, and was presented by Doctor 

 Felippone. 



This species is closely related to Mycetopoda legv/men von Martens 

 and naturally groups with it, but is much narrower in front and more 

 oblique. 



CORBULA URUGUAYENSIS. new species 



Plate 4, figures 7-9 



Shell rather thick, subquadrate, rounded in front, shortly truncate 

 at the rear, the left valve smaller than the right and closing into 

 it slightly. Dorsal line angularly arched, ventral margin slightly 

 curved, rounding regularly into the anterior margin, and making a 

 sharp angle with the posterior margin, the left valve more nasute 

 than the right valve. Anterior ridge rounded, posterior ridge 

 sharply angled ; posterior area in each valve flattened, biangulate on 

 the margin. Sculpture of many flattened, nearly regular, concentric 

 riblets and minor concentric striae. Left valve with a prominent 

 overhanging Mya-like chondrophore just back of the tip of the beak, 

 and a partly hooded, concave plate just in front of it to accommodate 

 the cardinal tooth of the right valve. Right valve with a large 

 lightly curved cardinal tooth and an obscure, shelflike chondrophore 

 just back of it. Color creamy-white where periostracum has dis- 

 appeared from most of the shell. In left valve periostracum remains 

 on the posterior area and in a narrow strip along the ventral margin. 

 It is brownish, is concentrically lamellate and scaly. 



The type (Cat. No. 368243, U.S.N.M.) measures: Length, 11 mm.; 

 height, 7 mm. ; diameter, 5 mm. It and four paratypes (Cat. No. 

 368244, LT.S.N.M.) come from Cape Santa Maria, Department of 

 Hocha, Uruguay, and were presented by Dr. Florentino Felippone. 



