36 CONCHOLOGY. 



ferior or respiratory one somewhat larger than the superior ; labial 

 appendages short and striated ; branchiae very long, narrow, 

 united, and prolonged throughout the extent of the tubular cavity 

 of the mantle ; only one large contractile muscle between the 

 valves ; at the point of junction of the mantle and tubes is a 

 muscular ring, in which is implanted a pair of corneo-calcareous 

 appendages. 



Shell. Thick, solid, very short or annular, open before and 

 behind ; valves equal, equilateral, angular and trenchant before, 

 only touching each other by the opposite edges ; no hinge ; a 

 considerable spoonlike cavity ; only one feeble muscular impression. 

 Tube more or less distinct from the substance in which the animal 

 lives, cylindrical, straight or winding, and closing with age at 

 the bucal extremity so as to envelope the animal and its shell ; at 

 the other end it is always open, and divided internally into two 

 syphons by a partition in the n^iddle. Inhabits the European 

 seas in timber. Three species. 



Teredo navalis. Teredo palmulata. Teredo gigantea. 



FAMILY II. 



Pholidahia. Two Genera. 



1. Genus Pholas. PI. VI. 



Anhnal. Without a tubular sheath, projecting anteriorly into 



two united tubes, frequently surrounded by a common skin, 



and the posterior extremity provided with a short muscular foot, 



flattened at its extremity. 



Shell. Multivalve, equivalve, transverse gaping at both ends, 

 with various accessory pieces either on the hinge or below it. 

 Inhabits Indian seas and American shores. Thirteen species. 

 Pholas dactyla. Pholas silicula. 



P. orientalis. P. costata.* 



P. Candida. P. callosa. 



P. dactiloides. P. clavata. 



P. papyracea. P. ovum. 



P. tuberculata. P. lancellata.* 



P. crispata. 



