- 16 - 



Oh araot eristic of higher latittides, suohas the forma v;hiGh frequent- 

 ly' form, entire beds in the Torlctov.n T'iocene, are conrjpionouG- 

 1^S ahseiit. Although individuals of the genus Spondriuij pre no"^ 

 numerous, they are divided among three soeaiec; the genus is 

 at present c'oniined to tropical or suhtropio al regions and is 

 relati'-ely rare in the Tertiar^.^ famias of the United States, 

 all of the ocourrences in the middle and later Tertiai'^: . faunas 

 hein- restricted to the U'lorid.ian area. 



Perha-ps the most obvious ind.ieatlon of temperature 

 conditions is furnished by ths Astartacea. I>/en the v/arm-water 

 Oaloosahetchie and '.Vaccaraaw famm ;-3' include one or two Astartes, 

 hut in the 3ov/den assemblage the genus is entirely absent, the 

 superfc-mily beiri^ represented only oj several Orassatellites, 

 including three species of the subgenus o r q o - ' -^ ^i i ?, . "'■'n^- -ponder- 

 ous valves of an Schinocharna , a ^-enus vvhieh is at the -resent 

 time oreSminently Antillean in distribution, are a very conspi- 

 cuous element. 



It has already been remarked that the extraordinary 

 development of the lucina.cea is to be considered one of t'-^e not- 

 able features and it is significant ;_..^^ the entire group is 

 O-iiite partial to tropical habitats, although a few species, 

 especially of the genus Divaricel] a , range into hi^h latitudes. 

 -0 other superfamily, e::cept the Arcacea, presents an equal 

 numbe 1- of species and from the point of view of the miniber of 

 gnera and sections among v.hieh the numerous species are distri- 

 buted this group i.. .^...urps.ssed. 



