328 piioladinjE. 



Genus NAVE A, Gray. 



Shell ovate, valves with the anterior gape not closed in 

 the adult by a callous plate, a small, transverse, posterior 

 plate under the coriaceous epidermis placed behind the 

 beaks ; hinge-plate produced and reflexed over the beaks. 



Ex. N. subglobosa, Gray, pi. 89, fig. 6, 6, a, 6, b. 



The small shells comprised in this group are usually 

 found embedded in sponge; in general appearance they 

 resemble Zirpluea, but the hinge-plate is produced and 

 reflexed over the beaks. 



Species of Navea. 



nucifera, 0. Fabr. tenuis, Gray. 



subglobosa, Gray. 



Genus PHOLADIDEA, Turton. 



Siphons with horny or shelly valves at their base, the 

 branchial siphon cirrhated, the anal plain at the end. 



Shell ovate, with the front gape large, at length closed 

 by a callous plate; dorsal valves two, small. 



Ex. P. papyracea, Solander, pi. 90, fig. 1. Shell, P. 

 papyracea, fig. 1, a, 1, b. 



Syn. Pholidea, Sivains. Talonella, Gray. Hatasia, 

 Gray. 



The shelly tube protecting the base of the siphons is 

 absent in young individuals; but in the adult it forms a 

 conspicuous, cup-shaped appendage which appears to be 

 entirely wanting in the other genera which have the anterior 



