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593 



TERTIARY FAUNA OF FLORIDA 



Oligocene of the Chipola beds, Calhoun County, Florida, Dall and Burns, 

 and of the Alum Bluff beds at Oak Grove, Santa Rosa County, Florida, 

 Burns. Miocene of Suffolk and Yorktown, Virginia; of Wilmington, North 

 Carolina, of the Natural Well, Duplin County, North Carolina, and of Dar- 

 lington, South Carolina; Burns and Harris. Pliocene of the Dismal Swamp, 

 Virginia; of the Waccamaw beds, South Carolina; of the Caloosahatchie 

 beds, Florida, on the Caloosahatchie, Alligator Creek, and Shell Creek ; John- 

 son, Burns, Dall, and Willcox. Recent in thirty to one hundred and fifty-five 

 fathoms on the southeast coast of the United States and in the Antilles and 

 on the Pacific coast of California. 



This widely distributed and ancient species is represented in the Oligo- 

 cene of Bowden, Jamaica, by L. bistdcata Guppy (non Whitfield). Like some 

 other species of the sub-genus Lanbiihis it is subject to a wide range of 

 variation in its external sculpture. This may be finely and regularly con- 

 centric over the whole surface, or partly obsolete towards the ends and base. 

 Occasional specimens are found in which the surface is nearly smooth and 

 others in which the fine concentric ribbing is replaced by a few distant, coarse 

 ribs or waves. In fact, the extremes are so discrepant that in the absence of 

 a connecting series almost any one would doubt that the shells could belong 

 to one and the same species. L. robusta Aldrich varies in a similar manner. 

 Other species of the same group, such as L. iaphria Dall {ccelata Hinds, non 

 Conrad) and L. peltcUa Dall, even when gathered in large numbers, show a 

 gratifying uniformity of character. Hence it follows that much caution 

 should be used in naming new forms from beds where named species of 

 this group are already known to occur. 



Genus YOLDIA Moller. 



This group appears to be, on the whole, more modern than the typical 

 Lcda, and occurs for the most part rather sparingly in the Tertiary. Though 

 the number of species is small, individuals are astonishingly numerous in 

 some localities, and one stratum at Shell Bluff on the Savannah River is 

 almost entirely composed of the fossilized valves of a single species of Yoldia. 

 After eliminating the Yoldiform species of Lcda, comparatively few species 

 remain to be discussed. Yoldia glacialis Wood, described from recent speci- 

 mens, was described from the Pleistocene of New England as Y. portlandica 

 Hitchcock, and is the Y. arctica of several authors, but not of Gray. Yoldia 



