14 PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 



The type is apparently a left valve and the right valve is probably very 

 similar with subequal ears and without a byssal notch, since there are about 

 twenty such valves in the collection, and there are no others of different 

 form that could be right valves of this species. . The form is like that of 

 the group for which Meek proposed the name Entolium, but it lacks the 

 diverging "teeth" characteristic of that subgenus. Similar forms are not 

 uncommon in the Jurassic and Cretaceous, such as Pecten operculifonnis 

 Gabb from the Lower Cretaceous Horsetown beds of California, which, 

 however, has broader ears and no radiating striae. 



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

 of cafion four miles east of Lake Pueyrrydon, and ten miles east of the 

 lake. The figured specimen is from the latter locality. 



PECTEN OCTOPLICATUS sp. nov. 



PI. IV, Figs. 2 and 3. 



Shell small, ovately subtriangular, conspicuously inequivalve, with eight 

 strong radiating ribs on each valve. Right valve very convex, with prom- 

 inent narrowed beak ; anterior ear elongate-triangular, with a deep byssal 

 notch beneath it ; posterior ear much smaller and inconspicuous ; ribs very 

 prominent, about as broad as the interspaces, subangular, each bearing 

 several obscure radiating lines and crossed by numerous fiae concentric 

 lines. Left valve much less convex, with subequal, rather broad triangu- 

 lar ears ; ribs more rounded, much less elevated and relatively more nar- 

 row ; the radiating and concentric lines also less conspicuous than on the 

 right valve. 



Height of an average specimen from beak to base 9 mm.; greatest 

 length at right angles to above measurement 8 mm.; convexity of right 

 valve about 4 mm., of left valve about 2 mm. 



Locality and position. Abundant in the Ammonite (Belgrano) beds at 

 mouth of cafion four miles east of Lake Pueyrrydon and represented by 

 three left valves apparently belonging to the species from the same ho- 

 rizon, ten miles east of the lake. 



AVICULA (OXYTOMA) TARDENSIS sp. nov. 



PI. IV, Figs. 6 and 7. 



Shell small, obliquely ovate, inequivalve ; length of hinge line not quite 

 equal to height of shell ; beaks rather prominent, extending beyond the 



