CONCHOLOGY. 37 



Tube more or less distinct from the substance in which the ani- 

 mal 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 middle. Inhabits the European 

 seas in timber. Three species. 



Teredo navalis. Teredo palmulata. Teredo gigantea. 



FAMILY II. 



Pholadakia. Two Genera. 



1. Genus Pholas. PI. VI. 



Animal. 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, flat- 

 tened at its extremity. 



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

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

 Inhabits the Indian seas and American shores. Eighteen species. 



Pholas dactyla. Pholas papyracea. 



P. orientalis. P. tuberculata. 



P. Candida. P. silicula. 



P. dactiloides, P. callosa. 



P. costata.* P. truncata.* 



P. clavata.* P. californica.* 



P. ovum.* P. penita.* * 



P. lancellata.* P. oblongata.* 



P. crispata.* P. cuneiformis.* 



2. Genus Gastrochseyia. PI. VI. 



Animal. Unknown. 



Always without accessory pieces, therefore easily distinguished 

 from the Pholas. 



Shell. Equivalve, somewhat cuneiform with a very large oval 

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