58 



14-294; Glycymeris pectinata, 2-175; Leda acuta, 7-225; Barbatia 

 Adamsii, 5-1 16; Phacoides aniantus, 2-640; usually shallow; Pha- 

 coidcs crenulatus, 15-124; Phacoides multilincatus, 8-287; Venen- 

 cardia tridentata, 36-124; Chione cribraria, 15-124; Turbonilla 

 interrupta, 2-107; Crcpidula aculeata var. costata, 0-589, commonly 

 0-25 ; Crcpidula plana, 0-487, usually shallow. Also, it must be 

 taken into account that Ptcria colymbus, Diplodanta semiaspera and 

 Venericardia tridentata are very rare forms, and that Leda acuta, 

 Glycymeris pectinata, Barbatia Adamsii, Chione cribraria, and 

 Crcpidula aculeata var. costata are almost as rare in the Pleistocene 

 of South Carolina. This fact could be interpreted to mean that these 

 forms may even have had their preferred habitat close to the lower 

 limit in depth, and yet a few individuals have lived in shallow water; 

 but we have record, in case of two of them, that they prefer the 

 shallower depths. Two other of these species are seen to have a 

 very wide geographical range: Turbonilla interrupta from Nova 

 Scotia to the Barbados, and Crepidula plana from Prince Edward 

 Island to Trinidad. Now, the general rule for a species migrating 

 southward is to seek the cooler waters it is accustomed to by sinking 

 deeper and deeper. The probability is that these two forms 

 reach their greatest depth range much farther south than along 

 the South Carolina coast. The other three species are all Pha- 

 coides, and it is well known that one of them, Phacoides amian- 

 tus, usually lives in shallow waters. Now, in the absence of con- 

 tradictory evidence, it is usually safe to assume that what is pre- 

 ferred by one species of a genus is probably preferred by the others. 

 So the three species of Phacoides may be considered as preferring 

 shallow waters. Of the seventeen forms having their maximum 

 depth range between fifty and one hundred fathoms, some are rare 

 and others very rare, and need not be given too much weight ; and 

 the others still have abundant opportunity, without an exception, of 

 having a much shallower habitat than fifty fathoms, almost all of 

 them having an upper range of eight fathoms or less. It seems true, 

 then, that on the whole these species today prefer a shallow water 

 habitat, many of them living between tides even, as the absence of 

 depth figures, following Dall, may generally mean. They constitute 

 what may be called a littoral facies. The conclusion from this study 

 of depth is that the Pleistocene species of South Carolina lived, on the 

 whole, in shallow water and constituted a littoral facies. The value 

 of this conclusion will be more evident later, when we come to con- 

 sider geographical range. 



