PART II. PHOLID^. 363 



extremity open, at the other closed by a plate which 

 is perforated with small holes, near to which are the 

 bosses : lives in sandy shores. {Jig. 1 J 4. /^ g.) 



A. vaginiferum Lam. Sow. Gen. f. 1. 2. 



Clavagella Lam. Two irregular valves placed within 

 a short shelly tube, dilated at its open extremity, and 

 to which one valve is fixed or soldered at the other : 

 perforates stones, &c. (^fig. 114. «, A.) 

 C. aperta. Sow. Gen. f. 1 — 4. 



Fistiilana Lam. Animal not perforating ; tube purse- 

 shaped, straight, the narrow extremity open, the other 

 closed; a transverse septum crosses the tube, and 

 incloses at its largest end a bivalve shell, which is 

 elongated, solen-shaped, gaping widely at the basal 

 margin, and united by a ligament, i^fig. 114. w.) 



F. clava. Sow. Gen. f. 1 — 4. 



Gastrochixa Lam. Animal perforating or parasitic ; 

 tube calcareous, clavate, nearly divided longitudinally 

 for half its length by an internal ridge, which forms 

 a double aperture; the other or thick extremity en- 

 closes an ovate bivalve shell, gaping very wide ante- 

 riorly ; hinge linear and marginal ; teeth none. {^fig. 

 114. 6, c,d) 



G. modiolina. Sow. Gen. f. 1.* 



Pholadomya Sow. Shell 115 



not tubular, pholas- 

 shaped, perlaceous, 



slightly gaping, no ac- 

 cessary valves ; ligament 

 short ; external hinge 

 with a small elongated pit somewhat triangular, and 

 a marginal plate on each valve ; umbones very close. 



P. Candida. Sow. Gen. Man. f. 57. {fig. 115.) 



Pholas Linn. Animal perforating but not tubular ; 



* I consider the perforating species to be types of a different sub-genus ; 

 and probably those which are parasitic upon other shells should likewise be 

 separated. 



