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TERTIARY FAUNA 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- 

 biana Goodall. 



Section Pcniiella Val., 1846. 



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

 plax confluent. Type Plwlas penita Conrad, 1838 (-|- P. concainerata Desh., 

 1840, -|- P. Conradi, Val., 1846). Pholai/ieria Conrad, 1865, is probably syn- 

 onymous. 



Section NcttasioincHa Carpenter, 1S65. 



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

 flaps. Type P. Darivini Sowerby (= P. penita Tryon, not Conrad). 



Section Hafasia Gray, 1851. 

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

 Type P. mdaniiya Sowerby (=; P. Wilsoiii Conrad, 1849). 



Genus PARAPHOLAS Conrad, 1S49. 

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

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

 sulci, 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 Plioladidca in not being an original secre- 

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



Genus MARTESIA Leach. 

 Martcsia Leach, in Blainville, Man. de Mai., i., p. 632, 1825. Type P. clavata Lam. = 

 Pholas striata 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 

 Pholads 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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