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671 



TERTIARY FAUNA OF FLORIDA 



Superfamily OSTRACEA. 

 Family OSTREIDy-E. 



Geuus OSTREA (L.) Lamarck. 



Type Ostrea edulis Linne. 



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

 Tertiaries, comprises several conchological groups. The typical Ostrea, 

 which is moncecious, 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 

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

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

 giiiica Gmel. and represented in the present European fauna by Ostrea angii- 

 tata 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 Eocene a fourth group may be added which seems to have left 

 no descendants. 



Subgenus Crassostrea i^diZco, 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. virginica Gmel. Eocene to recent. 

 Section Cyinbulostrca Sacco, 1S97 {Cnbitostrca Sacco, 1897). 



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

 usually of small size. Type 0. cyinbiila 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 MS. name I had used. It is to be regretted that the diagnosis offered by the author 

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



