48 Pelecypods of the Bowden Fauna [246 



The Prionodesmacea play an important role in the constitu- 

 tion, being represented by 79 species, or more than 40 per 

 cent of the fauna. The larger part of this number is contri- 

 buted by -the taxodonts, which include 44 species. The most 

 abundant taxodont is the genus Area, which has 28 species 

 distributed among 10 sections. The Scapharcas are the most 

 prolific, both individually and specifically. The section 

 Cunearca, which usually occupies a position of importance in 

 the mid-Tertiary faunas of the Antillean region and its peri- 

 meters, is represented by a single small form and the sub- 

 genus Noetia is entirely absent. Three species of Barbatia 

 are grouped in a new section that bears a relation to Barbatia 

 s. s. similar to the relation between Argina and Scapharca 

 s. s. Another Barbatia of unusual type has been provisionally 

 referred to Fossularca, although it probably represents a new 

 section. A minute Bathyarca is abundant in one of the col- 

 lections, but is rather rare in the other minute collections 

 available. 



Among the prionodonts the Pectens are subordinate only 

 to the Areas. They contribute 15 species representing seven 

 sections among which are included virtually all the groups of 

 a typical tropical fauna. The Aequipectens are the most 

 abundant and include several species that are widely distri- 

 buted in the Tertiary deposits of the Antillean region. With 

 regard to specific diversification Chlamys s. s. is comparable 

 to Aequipecten, but only one of the species is abundant. The 

 valves of a small delicate Pseudamusium s. s. are numerous 

 and the section Propeamusium is represented by a single 

 valve. 



The oysters form a puzzling assemblage. In all the collec- 

 tions the number of individuals is small and large forms are 

 notably absent. The small size is probably not without sig- 

 nificance when it is considered that one of the Bowden species 

 reaches an imposing size in the Alum Bluff faunas and especi- 

 ally in the Santo Domingan fauna. A similar relation 

 obtains for an unusually large and ponderous Santo Do- 

 mingan Spondylus. If the current synonymy for Ostrea 



