1 6 PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 



is broken off and some of the hard, sandy matrix still clings to a part of 

 the surface. 



The species may be compared with G. alpina Pictet and Roux, 1 which 

 is almost as large and somewhat similar in form, but is a straighter shell 

 and has a more distinct anterior wing. Gervillia dentata Krauss 2 from 

 the Uitenhage beds of South Africa is another large species that has some 

 general resemblance to this form, but it is not so thick shelled, the beak 

 is not so pointed and the shell is straighter. 



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

 of cafion four miles east of Lake Pueyrrydon. 



MYTILUS (?) ARGENTINUS sp. nov. 



PI. IV, Fig. 4. 



Shell small, elongate-ovate, moderately convex; beaks prominent, 

 slightly incurved ; dorsal margin slightly convex without definite posterior 

 angulation ; ventral margin nearly straight, posterior end regularly and 

 broadly rounded ; surface marked only by very fine growth lines and con- 

 centric wrinkles, which are inconspicuous except when magnified. 



Length of an average specimen from beak to base 8 mm.; greatest 

 breadth 5.5 mm.; convexity of the two valves about 6 mm. 



This little species has almost the form of a Crenella, and some obscure 

 radiating lines on a weathered specimen increased the resemblance and 

 led to its reference to that genus, when the collection was first examined. 

 Well-preserved specimens, however, show no radiating sculpture. 



Locality and position. The figured type and four other specimens are 

 from the Ammonite (Belgrano) beds at mouth of canon four miles east of 

 Lake Pueyrrydon, and one specimen from the same horizon ten miles east 

 of the lake. 



LlTHOPHAGUS Sp. 



This genus is represented in the collection by a single small flask-shaped 

 burrow in a fragment of oyster shell from the Ostrea horizon (Gio beds) 

 400 feet below the Ammonite layer at the mouth of the canon four miles 



'As figured by Pictet and Campiche, Terrain Cretace de Sainte Croix, pi. 155, figs. 2-4. 

 According to these authors the species includes the Cretaceous forms figured by Sowerby (Min. 

 Conch., pi. 511) under the name G. aviculoides but not belonging to that Jurassic species. 



2 Nova Acta, Vol. 22, p. 458, pi. 50, figs, \a-\c. 



