63 



But this is no more than was to be expected. Unless there had been 

 very unusual conditions of climate during the Pleistocene deposition, 

 a region in the latitude of South Carolina could hardly be expected 

 to have anything else than a southern facies of marine fauna. On 

 the other hand, it is somewhat astonishing to find that, out of the 160 

 species, only one has its southern limit at Hatteras or at some point 

 north thereof. This is Aligena elevata, and has its northern limit at 

 Maine, and southern at Hatteras, most abundant in the region just 

 south of Cape Cod on to New Jersey. Its depth range is 2-63 fathoms 

 so far as is known. The probability is that it will be found farther 

 south and in deeper water in some of the dredging that is being 

 done. As said at the outset, it is easier for a cold-water form to 

 move into warmer regions than for the opposite to take place. This 

 supposition carries more credence when it is noticed that its northern 

 range is only so far north as Maine, and its deepest depth range only 

 sixty-three fathoms. Furthermore, its extreme rarity as a Pleisto- 

 cene fossil in South Carolina, only one valve being found from several 

 bushels of the material collected, would lead one not to attach too 

 much importance to its being found in the Pleistocene so far south. 

 There is a pelagic form described by Holmes under the name Cavo- 

 linia Tuomeyii, which has been questionably included in these tables 

 as Cavolinia gibbosa, whose range limits are 43 N. to 41 ° N. This 

 form cannot enter into the discussion ; so likewise several other ques- 

 tionable forms. Turning again to the tables, it is seen that there are 

 several species that may possibly be regarded as northern forms, 

 though they do range farther south than to Cape Hatteras. These 

 are : Venus mercenaria var. notata, Cape Cod to Georgia ; Petricola 

 dactylus, Maine to South Carolina; Macoma balthica, Arctic Sea to 

 Georgia; Mya arenaria, Nova Scotia to South Carolina; Bamea 

 truncata, Massachusetts to South Carolina ; Solcn viridis, Rhode 

 Island to Georgia ; Scala midtistriata, Cape Cod to South Carolina ; 

 Turbonilla nivea, Maine to South Carolina ; Polynices heros, Gulf of 

 St. Lawrence to Georgia (on authority of Verrill) ; Chiton apicida- 

 tus, Massachusetts to South Carolina. But every one of these is 

 seen to reach as far south as South Carolina, some beyond. If they 

 do that today, there is no reason why they should have required a 

 different climate in Pleistocene times to reach the latitude of South 

 Carolina. Furthermore, the tables show that almost all these forms 

 are shallow-water forms, as already discussed, and could have mi- 

 grated southward more easily under a cooler climate than under a 

 warmer one. If the climate had been much cooler in Pleistocene 



