98 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



Remarks: Our fragments from Santa Cruz do not show the external 

 form of the shell. According to v. Ihering it is subquadrate, a little 

 broader than high. The specimens from Lake Pueyrredon are chiefly 

 casts ; one of them shows clearly the impressions of the lower margin of 

 three of the cardinal grooves (see pi. XXIV., fig. 2*), agreeing with the 

 specimens from Santa Cruz in being very broad and distant, which is the 

 most prominent character of this species. Only part of the shell remains 

 here. The casts indicate apparently a higher shell, but taking into con- 

 sideration the great thickness of the shell at the anterior end, and the 

 missing part at the posterior, which has been lost by fossilization, the 

 outline of the Pueyrredon specimens would come near to that given by 

 v. Ihering. I do not hesitate to refer them to v. Ihering's species, since 

 the characteristic feature of P. quadrisulcata is exhibited in one of them. 



Record of specimens : Mouth of Santa Cruz River, 9 fragments; Lake 

 Pueyrredon, base of Tertiary, 2 sp.; Lake Pueyrredon, 600' above base, 

 4 sp. (2 of them young). 



Distribution: La Cueva, upper part of Patagonian formation (v. Ih.). 



Affinities : No known species of Perna can be compared with this one ; 

 but there is some resemblance to Crenatula aviculifonnis Philippi (Navidad 

 beds of Chili), but the latter is too incompletely known to permit any 

 opinion in this respect. 



Fam. OSTREWsE Lamck. 



Gen. OSTREA L. 

 33. OSTREA TORRESI Philippi. 



PI. XIV, Fig. 3"'". 



1887 O. torr. Philippi, Tert. Quart. Verst. Chiles, p. 215, pi. 48, f. 8. 

 1899 O. torr. Ortmann, in: Amer. Journ. Sci., v. 8, p. 427. 



Shell in outline broader or narrower oval, rarely suborbicular ; mod- 

 erately thick. Lower valve deeply excavated, upper valve flat. Area 

 moderately large, triangular. Muscular impression about in the middle 

 of the inner surface, only slightly lateral. Both valves with numerous, 

 strong radial plaits, but on the upper valve these are less distinct and 

 sometimes missing. 



Measurements: Length, 104, 117, 125, 131. An upper valve : 129 mm. 

 Width, 74, 1 06, 74, 95. 102 mm. 



