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671 

 TERTIARY FAUNA OF FLORIDA 



Superfamily OSTRACEA. 

 FAMILY OSTREID^. 



Genus OSTREA (L.) Lamarck. 



Type Ostrca c dulis Linne. 



The genus Ostrca, as restricted by Lamarck and represented in our 

 Tcrtiaries, comprises several conchological groups. The typical Ostrca, 

 which is monoecious, producing large embryos which are incubated for a 

 considerable period in the parental gill-lamina;, is not known to occur in 

 America. Our common oysters belong to a group characterized by being 

 dicrcious and discharging the seminal products directly into the water, which 

 must take the name of Crassostrea Sacco.* This is typified by Ostrca vir- 

 ginica Gmel. and represented in the present European fauna by Ostrea angit- 

 lata Lam., known there as the Portuguese oyster. It being impracticable to 

 determine the affinities of the fossil oysters with relation to these two sub- 

 genera, they will be considered here under the common generic name. It is 

 not improbable that all the American oysters belong to the subgenus Crass- 

 ostrea. 



Conchologically, the ostrean element of the American invertebrate fauna 

 presents three types which exist in the present fauna and may be traced 

 throughout the Tertiary, their outlines becoming less sharp as we recede in 

 time. In the Kocene a fourth group may be added which seems to have left 

 no descendants. 



Subgenus Crassostrea (Sacco, emend.) Dall (+ Gigantostrca Sacco, 1897). 

 Valves discrepant, the upper valve smoother, the lower valve coarsely and 

 irregularly plicate, with the distal margins little if at all crenulated, the hinge- 

 margin not alate, the apices straight or oblique but not spirally twisted. 

 Type 0. virgiiiica Gmel. Eocene to recent. 

 Section Cynibitlostrca Sacco, 1897 (Cubitostrea Sacco, 1897). 



Shell with the plications of the lower valve regular and fine, species 

 usually of small size. Type O. cyinlntla Lamarck. Eocene. 



It is a curious commentary on the distance from nature attained by a 

 certain school of systematists, that their classifications enable them to put 



* This name has been published since the present revision was completed, and is therefore sub- 

 stituted for the M.S. name I had used. It is to foe regretted that the diagnosis offered by the author 

 of Crassostrea has no systematic value and is even opposed to the facts. 



