Paleontology Zorritos Formation 17 



acters, or indicative of progressive change from one type to 

 the other, oflfers further evidence of the transition between 

 the sections, and adds to the list of illustrations which show 

 the completeness of the gradation between them. 



Tlie presence of the subgenus Xoetia is of interest in its 

 addition to the Miocene occurrence of that group, which is 

 distinctively American in fossil distribution. Grzybowski 

 described a species, A. (Xo'ctia) modcsta, from Zorritos 

 which is apparently different from Area cholana, and an- 

 other unstudied Xoetia occurs in a collection of stratigraph- 

 ically unlocated fossils from Peru which, by inference 

 from the locality labels, may have come from the Zorritos 

 formation. The absence of the subgenus Area s. s., an 

 element normally to be expected in a fauna such as this, 

 means little as yet. 



The one Pecten, P. n'oodringi^ is of the small, tropical 

 type. Anomia berryi is interesting on account of its size 

 and weight ; the Upper Zorritos and X'ariegated habitats at 

 which this species has been found must have been peculiarly 

 favorable. 



One of the striking characteristics of the Lower Zorritos 

 faunule from Quebrada Zapotal is the abundance of Cras- 

 satellites berryi n . sp.. a distinctive type, undoubtedly repre- 

 senting a peculiar divergence from the ancestral strain of 

 C. gibbosus Sowerby, now living on the Peruvian coast. 

 C. nelsoni (Grzybowski) probably represents the stock 

 which preceded C. gibbosus in direct genetic line. 



The occurrence of dementia dariena Conrad, a member 

 of a genus with sparse fossil and not much wider recent 

 distribution, is worthy of note. This species is known so 

 far only from Panama, Costa Rica and Peru, and its clear 

 identity makes it a conspicuous element, despite the fact that 

 it is not known to be abundant. It is unfortunate that the 

 stratigraphically located specimens of C. dariena in the 

 present collection are not well preserved, the ones in the 



