STANTON I THE MARINE CRETACEOUS INVERTEBRATES. 1J 



east of Lake Pueyrrydon. The burrow, which is rilled with calcareous 

 sand and probably still contains the shell, measures 10 mm. in length and 

 5 mm. in greatest diameter. 



PINNA sp. 



A single small Pinna in the collection is too imperfect for specific de- 

 scription. The shell is rather slender, moderately convex, not carinate, nor 

 distinctly angular on the median line, with the upper two thirds of the 

 shell marked by 10 or 12 radiating lines and the rest of the surface bear- 

 ing irregular, less conspicuous lines of growth. The specimen, which is 

 probably not a mature shell, measures 90 mm. in length, 28 mm. in great- 

 est breadth and 10 mm. in convexity of both valves. 



Compared with P. robinaldina d'Orbigny, which Behrendsen 1 has re- 

 ported from the Lower Cretaceous of the Argentine Republic, this species 

 may be easily distinguished by its more slender and less convex form and 

 by the absence of a median angulation. It much more closely resembles 

 the Upper Cretaceous P. lakesi White 2 from the Fort Pierre formation of 

 Colorado. 



Locality and position. From the Ammonite (Belgrano) beds ten miles 

 east of Lake Pueyrrydon. 



NUCULA PUEYRRYDONENSIS Sp. nOV. 

 PI. IV, Figs. 8 and 9. 



Shell of medium size, elongate subovate, moderately convex; beaks 

 nearly terminal at the posterior end, which is almost vertically truncate ; 

 dorsal margin slightly convex ; anterior end broadly rounded, most promi- 

 nent above, passing below into the convex ventral margin ; surface nearly 

 smooth, bearing very fine, closely arranged lines of growth, with a few 

 more conspicuous concentric furrows at wide intervals. 



Length 17 mm.; height 12 mm.; convexity of the single valve about 

 5 mm. 



The species is quite similar in form and surface to N. simplex Des- 

 hayes, from the Neocomian of France, as figured by d'Orbigny, 3 except 

 that its anterior end is more broadly rounded. 



1 Zeitschr. Deutsche Geol. Gesellsch., Bd. 44, p. 25, 1892. 



2 12th Ann. Rep. U. S. Geol. and Geog. Surv. Terr., pt. I, p. 17, pi. II, fig. i, 1880. 



'Paleont. Franq. Terr. Cret, t. Ill, pi. 301, figs, u and 12. 



