22 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



or ten large smooth ribs, that radiate from the beak and are broader than 

 the interspaces. 



ASTARTE PERALTA Sp. nOV. 

 PI. V, Figs, i and 2. 



Shell very large and massive, ovate, moderately convex, considerably 

 higher than long, with prominent submedian beaks, from which the outline 

 descends rapidly and almost equally, with a gentle convex curve behind, 

 and concave in front to the extremity of the lunule, which is rather large 

 and deeply excavated with abrupt walls ; ventral margin regularly rounded; 

 surface marked by fine lines of growth and by rather prominent concen- 

 tric ridges, which are less prominent on the middle of the valve than 

 toward the ends, and become broader and less conspicuous toward the 

 ventral margin of the adult; hinge broad and massive, showing in the 

 right valve a small anterior cardinal tooth, a very large middle cardinal, 

 two large sockets for the reception of the cardinals of the left valve, 

 and traces of anterior and posterior laterals ; posterior cardinal not de- 

 veloped. The free border of the shell is not crenulated on the interior. 



Height 125 mm., length 101 mm.; convexity of both valves about 

 80 mm. 



This description is drawn from a well-preserved right valve showing 

 all the essential specific and generic features, though a fragment has been 

 broken from the posterior end. There is another imperfect specimen 

 showing the beak of a left valve. 



The species is distinguished by its large size and its great height, as 

 compared with its length. In these features it recalls some of the gigan- 

 tic species of Astarte from the Jurassic, such as Astarte damesi Boehm, 1 

 though differing from them in outline and other details. 



The growth lines of A. peralta show that its height, as compared with 

 the length, increases rapidly with age and these two dimensions are equal 

 at least until they reach 25 mm. At that size the shell resembled A. 

 Postsulcata, except that the sculpture was considerably coarser and the an- 

 terior end was less prominent. 



Locality and position. From the (Belgrano) Ammonite beds at mouth 

 of cafion four miles east of Lake Pueyrrydon. 



1 Palaeontographica, Supplement II, Die Bivalven der Stramberger Schichten, p. 561, pi. 63, 

 figs. 1-3. 



