2 CONCHYLIX—DITHYRA. 1. 



Some of them, however, have the valves strengthened by 

 accessorial ones, placed about the hinge or in front; and some 

 are merely united by a strong elastic membrane. 



These accessorial valves form no part of the necessary generic 

 character, as some of the species are entirely without them, and 

 in others they vary both in number and shape. 



From the Teredo this genus differs, both in the shape of the 

 shell, which is transversely elongated and oval, and in wanting 

 the cylindrical tube with its accessorial appendages. 



# Valvis stilco longitudinali divisis. 1-4. 

 The valves divided by a longitudinal groove. 



papyracea. puoj^^g iestd clavatd, latere antico clauso obtusissimo, postico 

 hiante truncato accessorio producto annulari. 

 Shell club-shaped, closed and very obtuse at the anterior end, 

 open and truncate at the other end, which is furnished with a 

 produced accessorial ring. 



Tab. nost. 1. fig. 1 to 4. 

 Pholas papyraceus. Solander, Manuscripts. 



Portland Catalogue, p. 82, lot 1828. 

 Pholadidea Loscombiana. Turton, Conch. Diet. p. 147. 

 Mus. nost. In Torbay. 



Shell three quarters of an inch long, and an inch and three 

 quarters wide including the ring, in color and appearance resem- 

 bling whitish brown paper : the anterior end inflated, very obtuse 

 and rounded, closed when the valves are shut, and quite smooth 

 or about half its surface : the hinder half marked with close-set 



