308 Gardner — Relation of the Late Tertiary Faunas 



in Virginia and North Carolina was probably governed more 

 by temperature than by time, although the recent represen- 

 tatives are too distantly related to offer any definite proof. 

 Thracia conradi Couthouy, ranging on the east coast from 

 Labrador to Hatteras, is well known in the Yorktown, while its 

 presence south of that region, either in Tertiary or Recent 

 times, is exceedingly doubtful. The Yenericardias are prolific 

 throughout the Miocene and early Pliocene, but the more 

 northern race, Venericardia gramtlata Say, which is present 

 in the Recent seas from Hudson Straits to Hatteras, dominates 

 in the Yorktown, which V. tridentata Say and V. perplana 

 Conrad, both of them denizens of the waters between Hatteras 

 and Charlotte Harbor, Florida, equal or exceed the northern 

 species in abundance during the Duplin and Waccamaw. 



The absence of any representative of the genus Echinochama 

 is probably due to latitude rather than time, since a species 

 very closely allied to JE. arcinella is abundant in the Oligocene 

 (Bowden beds) of Jamaica. Area (Fossularca) adamsi 

 Smith, which is well represented in the warm water faunas 

 from the late Oligocene on through the Duplin and the Wac- 

 camaw to the Recent, is absent in the Yorktown. The very 

 marked dissimilarity between the Cardiums north and south 

 of the Hatteras axis is probably due, in large part, to differences 

 in temperature since two of the three Yorktown species have a 

 meagre representation in the Duplin, while the more ornate 

 southern races are unknown in the Yorktown. Dosinia 

 elegans Conrad, a species ranging from Hatteras to Aspinwall, 

 is present in the Miocene at Alum Bluff, and was quite 

 abundant during the Duplin, although it was unable, ap- 

 parently, to extend its range northward into the cooler 

 waters of the Yorktown basin. In most of the Veneracea, 

 however, and in the Tellinacea, the cleavage in species seems 

 to be along formational lines rather than climatic, in spite of 

 the fact that the majority of the species are denizens of the 

 between tides or littoral zone, and so would be exposed to 

 climatic conditions more than those forms which dwell in a 

 more stable habitat. 



The gastropod fauna of the Virginia and northern North 

 Carolina Miocene is, on the whole, much less prolific than the 

 pelecypod, and much less evenly developed. The Terebras, 

 the Cones, and the Pleurotomids, all of them prolific south of 

 Hatteras, even in the Oak Grove sand member of Alum Bluff 

 formation of Florida and the Bowden marls of Jamaica, have an 

 exceedingly meager representation, both in species and individ- 

 uals, north of Hatteras. The Marginellas, on the other hand, a 

 cooler water group, are much more abundant in individuals north 

 of Hatteras than they are south of it. Fasciolaria, represented 



