6 4 



times than today, these species would probably have pushed their 

 way farther southward and be found in the Pleistocene deposits of 

 Florida. A search into the Florida Pleistocene fossil list fails to 

 show a single one of them there. So the supposition that the Pleis- 

 tocene climate for South Carolina was cooler than that today loses 

 this evidence. To offset these seemingly northern forms, we find a 

 few species with northern limit on the South Carolina shore and 

 ranging to the southward, namely : Cyrene caroliniana, South Caro- 

 lina to Cuba; Mytilus exustis, Charleston to Brazil; Xylotria palmi- 

 lata } South Carolina; Pyramidella crenulata, South Carolina to St. 

 Thomas ; Cochliolepis nautiliformis, South Carolina to Florida Keys. 

 These are shallow-water forms even in their most southern range, 

 and could not migrate far northward, according to the principle pro- 

 posed at the beginning of the discussion of depth. Their northern 

 range would be more limited under colder climate. Of the ten 

 forms named as possible northern forms, eight are rare in their oc- 

 currence in the South Carolina Pleistocene, and the other two are by 

 no means abundant. Of the five forms ranging from South Carolina 

 southward, four are rare in the Pleistocene, but the fifth, Pyramidella 

 crenulata, is abundant. This may be taken as a slight indication that 

 these warm-water species were more at home in the region than were 

 the species from cooler waters. 



One more comparison, and then the general conclusions can be 

 drawn. It is seen that three forms have their southern limit a little 

 to the north of South Carolina, but still south of Cape Hatteras. 

 These are Yoldia limatula, with a range from Norway to North Car- 

 olina; Modiolus modiolus, from the Arctic Sea to North Carolina, 

 and Mytilus edulis from the Arctic Sea to Fort Macon, North Caro- 

 lina. They are very rare in their occurrence in the beds under discus- 

 sion. It is not unreasonable to suppose that, if these species had 

 vitality enough to survive after rounding the Cape, they may have 

 pushed their way farther south still. It may be said of them, as it was 

 said of Aligena elevata, that it can be expected that dredgings will 

 reveal them farther south than they have yet been found. To compare 

 with these, there are six or seven species that have their northern limit 

 to the south of South Carolina. These one may, in this connection 

 call extreme southern forms. One of them, Sportella constricta, is 

 questionably included in the tables, and will not be considered, as no 

 correct conclusion could be drawn from questionable data. The 

 other six are: Diplodanta soror, Tortugas to Jamaica; Cyclinella 

 tennis, Cedar Keys, Florida, to Brazil ; Cardita floridana, Tampa to 



