18 CO^Cliy U A.— niTHYR A. 3. 



with a tube of adhesion, by which it attaches itself firmly to the 

 outer case. 



The principal points of discrimination between this genus and 

 that of the Pholas are, not merely the want of accessorial valves, 

 as has been usually supposed, but the essential difference of the 

 teeth, and in being furnished with a strong permanent coriaceous 

 ligament uniting the valves together. 



pholadia. Gastroch^ena volvis latere antico postice conniventibus, umho- 

 nibus subterminalibus prominulis. 

 Shell with the valves closing together behind at the anterior end, 

 the beaks nearly terminal and rather prominent. 

 Tab. nost. 2, fig. 8 and 9. 

 Gastrochaena cuneiformis. Spengler, ii. p. 179, fig. 8 to 11. 

 Pholas hians. Chemnitz, x. p. 364, tab. 172, fig. 1678 and 



1679. 

 Mya dubia Pennant, Brit. Zool. iv. p. 165, tab. 47. 



Turton, Linn. Syst. iv. p. 179. 

 Dorset Catal. p. 27, tab. 1, fig. 1 1. 

 Ltinn. Trans, viii. p. 33. 

 Donovan, Brit. Shells, iii. tab. 108. 

 Turton, British Fauna, p. 146. 

 Wood, Couch, p. 102, tab. 25, fig. 2 and 3. 

 Turton, Conch. Diet. p. 104. 

 Mya pholadia. Montagu, Test. Brit. p. 28 and 559, and 



suppl. p. 20. 

 Mytilus ambiguus. Dillwyn, Descript. Catal. p. 304. 

 Chama parva. Da Costa, Brit. Conch, p. 234. 

 Mus. nost. In rocks and stones, Torbay. 



