FAMILY 2. PHOLADARIA. 39 



Family 2. PHOLADARIA. 



Testa tubo nullo, sed partibus accessoriis testaceis ssepiiis instructa, an- 

 tice hiantissima. 



This is another family of terebrating Tropiopoda, closely allied to the 

 Tubicola, but differing in as much as the animal does not form a testa- 

 ceous tube ; yet, although it is wanting, some analogy may be traced in 

 the appearance of certain accessory testaceous pieces, entirely foreign to 

 the shell, varying in size and number according to circumstances : in 

 some species there is also a coriaceous or horny tubular appendage at 

 one end. We include but two genera, 



Xylophaga. 

 Pholas. 



XYLOPHAGA, Turton. 



Testa orbicularis, pequivalvis, inasquilateralis, antice hians, partibus 

 accessoriis testaceis duabus, subtrigonis, dente cardinali minuto 

 costaque interna, ab umbone ad marginem basalem utriusque valvar 

 decurrente. Impressiones musculares duo ; postica magna, obo- 

 vata ; antica minor, margini superiori imbuta. 



The shell of Xylophaga approximates closely in its general structure 

 to that of the last genus of Tubicola ; the valves being equal, inequi- 

 lateral and very much gaping, are very similar in form to those of Te- 

 redo, but in place of the calcareous tube, they are merely furnished with 

 two small accessory calyciform testaceous pieces, placed on the anterior 

 side of the hinge. There is a small curved tooth in each valve, with an 

 internal rib running from the umbo to the basal margin ; and there are 



