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THRTIARY I%UNA OF FLORIDA 



Subgenus PHOLADIDEA s. s. 



Shell with a double, rather small, protoplax, the siphonoplax cup-like, 

 the other accessory plates wanting; a single radial sulcus. Type P. Loscom- 

 bnina Goodall. 



Section l'?nitfllii Val., 1846. 



Like Pholadidca, but with a small mesoplax, the two parts of the proto- 

 plax confluent. Type Pkolas penita Conrad, 1838 (-f- P. concamerata Desh., 

 1840, + /'. Conradi, Val., 1846). Pholaineria Conrad, 1865, is probably syn- 

 f onymous. 



Section Nettastomelia Carpenter, 1865. 



Like Pholadidea, but small, with the siphonoplax prolonged as diverging 

 flaps. Type /-*. Darnnni Sowerby (= P. penita Tryon, not Conrad). 



Section ffaiasia Gray, 1851. 



Like Pholadidea, but with the siphonoplax prolonged into a shelly tube. 

 Type P. mclanura Sowerby ( P. Wilsoni Conrad, 1849). 



Genus PABAPHOLAS Conrad, 1849. 



Shell with a single large protoplax, the mesoplax and metaplax present, 

 double but confluent; a double hypoplax present; valves with two radial 

 surci, the posterior becoming obsolete with age; the siphonal prolongations 

 thin and horny, not attached to a heavy calcareous tube, which is formed 

 from debris by the animal around the siphonal opening of its excavation ; 

 this differs from the siphonoplax of Pholadidea in not being an original secre- 

 tion of the animal. Type P. californica Conrad (-f- P. Janellii Desh.). 



Genus MARTESIA Leach. 



Mttrd-siii Leach, in lilainvillc, Man. de Mai., i., p. 632, 1825. Type /'. ctavata Lam. = 

 /'/in/us stritila Linne. 



Shell with a large protoplax, elongated metaplax, and a double confluent 

 narrow hypoplax ; mesoplax and siphonoplax wanting ; valves with a single 

 radial sulcus. 



This is one of the oldest and most prolific groups of Pholads, both in 

 the Tertiary and existing faunas. 



The mutations which occur between youth and the adult condition in 

 1'holads are so great that the young shell may sometimes be referred with 

 equal plausibility to several genera, hence the references of our Tertiary forms 

 following must be taken as merely provisional. 



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