52 Pelecypods of the Bowden Fauna [250 



seas. The Bowden species are such as would be expected in 

 tropical waters ; indeed a number of them are encountered in 

 the present West Indian fauna. The genus Pecten is usually a 

 conspicuous element in the Tertiary and Eecent faunas of all 

 latitudes, but the large species that are characteristic of higher 

 latitudes, are absent. Spondylus is confined to tropical or 

 sub-tropic regions in the Eecent seas. In the middle and late 

 Tertiary faunas of the United States the genus is restricted to 

 rare occurrences in the Meridian region. Perhaps the most 

 obvious indication of the temperature of the waters is fur- 

 nished by the superfamily Astartacea, which is represented 

 only by several Crassatellites. Even the warm-water Caloosa- 

 hatchie and Waccamaw faunas include one or two Astartes, 

 but in the Bowden assemblage the genus is entirely absent. 

 An Echinochama, a genus which is preeminently Antillean, 

 is the most ponderous bivalve in the fauna. The entire group 

 of lucinoids is quite partial to tropical waters, although a few 

 species, especially of the genus Divaricella, range into high 

 latitudes. By far the greater number of the Cardiums are of 

 the ornate type that indicates a warm-water habitat. More- 

 over, the smooth or relatively simple forms are identical with, 

 or closely related to, Eecent species that do not occur north of 

 Florida. Although the distribution of the genus Tellina is 

 almost world-wide the group is predominantly tropical. 



In attempting to determine the depth of the water from a 

 consideration of the bathymetric range of identical or closely 

 related Eecent species a rigid adherence to the evidence fur- 

 nished by dredging records would often lead to absurd con- 

 clusions. An example is furnished by the genus Limopsis, of 

 which two species are present. According to available data 

 the group as a whole is characteristic of deeper water, yet 

 several species occur in Eocene beds of the Gulf Coast that 

 undoubtedly were deposited in very shallow water. 



The fauna is essentially a shallow- water fauna. All of the 

 Eecent species occur in water of shallow depth and many have 

 been recorded from the intertidal zone, but the range of sev- 



