6 PEOCEEDINGS OF THE U. S. NATIONAL MUSEUM vol.74 



NUCULA FELIPPONEI, new species 



Plate 4, figures 10-12 



Shell oblique, its dorsal margin sharply arched, its ventral margin 

 regularly curved, anterior margin long and gently sloping ; posterior 

 margin very short, abruptly descending, making a prowlike point 

 at its junction with the ventral margin. Beaks far back, about 

 3 mm. in front of extreme posterior end, and 12 mm. to the rear of 

 the extreme anterior end, curving backward, cordate, an elongated, 

 deeply impressed, heart-shaped escutcheon below them. Anterior 

 area flattened, anterior ridge well marked, but rounded. Sculpture 

 of many obscure concentric striae of growth, the rest periods some- 

 what emphasized. Periostracum very smooth and shining, paperlike, 

 tending to peel off, its color light olive at the beaks, darker olive on 

 the disk, becoming straw color near the margin. Chondrophore 

 spoonlike, overhanging in each valve, pointing toward the postero- 

 ventral margin, free from the posterior margin, but attached by a 

 portion of its edge to the anterior margin. Interior white, pearly, 

 appearing to be radially striated, the anterior margin with about 20 

 pearly teeth and the short posterior margin with 11. Margin not 

 crenulated. Anterior adductor scar lightly impressed, the posterior 

 one deep. 



The type (Cat. No. 368245, U.S.N.M.) measures: Length, 12 mm.; 

 height, 12 mm. ; diameter, 8 mm. It was taken from the stomach of 

 a fish — a croaker — in South America called a Corbina, Micropogon 

 undulatms Linnaeus, in the Rio de la Plata, Uruguay, and was pre- 

 sented by Doctor Felippone. Cat. No. 368246, U.S.N.M. includes 

 three paratypes. 



NUCULA URUGUAYENSIS, new species 



Plate 4, Figures 13-15 



Shell very oblique, sharply rounded at the front, widely rounded 

 at the rear. Dorsal margin angularly arched, posterior margin short, 

 truncately sloping ; anterior margin long, lightly arched, gently slop- 

 ing. Beaks set far forward, almost directly above the posterior mar- 

 gin; curving backward a distinct lunule below them. Escutcheon 

 transversely fluted with curving, waving, somewhat interrupted 

 granulose riblets. Anterior area with numerous flutings of the same 

 nature, disposed to bifurcate at the anterior ridge. Anterior margins 

 and margins of escutcheon obscurely scalloped, ventral margin in- 

 ternally finely, closely crenulated. Sculpture of close, flat concentric 

 striae, the grooves between them linear and clean-cut. Whole surface 

 microscopically radiately striate. Interior white, pearly. Posterior 

 teeth 7 in number, anterior 13. Chondrophore an elongate wedge- 



