206 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



dary spiral ribs are wanting, exactly as in P. Carolina, but the ribs are 

 more numerous (in a much smaller specimen figured by Speyer 30 are 

 present), and the longitudinal striae are less crowded. 



All other species differ more considerably, especially those forms desig- 

 nated under the name of/*, condita Brongn. (Hoernes, 1856, p. 270, pi. 

 28, f. 4-6), from Miocene to Recent, and P. reticulata Lmck. (Hoernes, 

 ibid., p. 268, pi. 28, f. 1-3, and Speyer, 1864, p. 185, pi. 33, f. 12), 

 from Oligocene to Recent, in which between the principal spiral ribs 

 one or more secondary ones are regularly intercalated, and in which 

 the longitudinal striae are rib-like, stronger, and more distant from each 

 other. 



It is extremely significant, that the present species compares better with 

 the Miocene P. pyriformis from California, than with any other species, 

 and especially that it does not exhibit the characters of those forms (P. 

 condita, reticulata} which continue to the Recent time. 



Fam. TRITONID^ Ad. 



Gen. TRITONIUM Lmck. 

 136. TRITONIUM BICEGOI v. Ihering. 



PI. XXXIII, Fig. 15. 



1899 T. b. v. Ihering, in: N. Jahrb. Miner., etc., v. 2, p. 29, pi. i, f. 8. 



Shell ovato-conical, swollen below, with three varices. Whorls with 

 fine spiral striae, and large tubercles, the latter, on the last whorl, in three 

 spiral rows, those of the upper row larger (6-7 between two varices), 

 those of the lower rows smaller, situated on two indistinct spiral ribs. 

 Columella smooth, canal short, a little twisted and oblique. Outer lip 

 subdentate, near the upper end with a distinct canaliform emargination, 

 opposite to which, on the upper part of the inner lip, there is a dentiform 

 fold. 



Height of incomplete individual : 76 mm ; diameter, 49 mm. 



Remarks: In our individuals the canal appears to be long, but the last 

 whorl is almost completely gone. 



Record of specimens : Mouth of Santa Cruz River, 2 sp. 



Distribution: Santa Cruz, Patagonian formation (v. Ih.). 



