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1423 



TERTIARY FAUNA OF FLORIDA 



metres in height, while the typical V. ascia when adult is commonly eighty. 

 This tends to intergrade with the variety laticardo. 



Claibornian Stage. 



Lower Claibornian Substage. — In this we find the varieties densata and 

 Hornii. 



Claiborne Sands. — Here we have the J', ascia with numerous mutations, 

 including nearly typical planicosta occasionally. 



Jacksonian Stage. — Here we have the Claibornian forms reproduced but 

 usually less vigorous, smaller, and more compact. Except in these respects, 

 which nevertheless give a local aspect to the Jacksonian shells, this horizon 

 repeats the mutations of the Claibornian. 



It may also be noted that several types forming distinct species seem to 

 branch off from the planicosta stock in the Lignitic, yet so far I do not find 

 these sustaining themselves beyond the stage in which they originate. Such 

 are V. marylandica Clark and V. potapacoensis Clark from the Nanjemoy and 

 Fort Washington horizons. The former is the V. planicosta, form a, of Harris, 

 op. cit., but it is distinct and the analogue of V. pectuncularis of the Parisian 

 Eocene and not of the V. planicosta. The latter, which is small, oblique, and 

 peculiarly pinched off behind, does not appear to have any exact analogue in the 

 European beds and has been obtained onh' in Maryland. 



Venericardia alticostata Conrad. 

 Cardita alticostata Conrad, Am. Journ. Sci., ist Ser., xxiii., p. 342, 1833; Morton's Synops. 



Org. Rem., App., p. 7, 1834. Claiborne sands. 

 Venericardia Sillimani Lea, Contr. Geo!., p. 69, pi. ii., fig. 47, i833- Claiborne sands. 

 Venericardia transversa Lea, Contr. Geo!., p. 68, pi. ii., fig. 46, 1833. 

 Venericardia alticosta Conrad, Checkl. Eoc. Fos. N. Am., p. S, 1866. 



Eocene of the Claibornian and Jacksonian series in Alabama and Louisiana. 



This form represents the finest development of the ancestral strain of 

 Venericardia from which the planicosta type is a lateral offshoot. This is 

 shown by the umbones of planicosta, which have the beaded or serrate and 

 terraced ribs of the alticosta type which are lost with growth. I am compelled 

 to differ with Professor Harris, who has united the Midwayan species with 

 alticosta. On the contrary, it seems to me that V. perantiqua Conrad (V. sub- 

 quadrata Gabb, not Conrad) is sufficiently distinct both in sculpture, size, and 

 general appearance, though the Midwayan specimens are rarely well preserved. 



