GINGLYMACONCHA. PHOLEOBIADZ. 257 
Inhabits the south-western coasts of England, where it is 
found burrowed in old oyster shells and detached portions of 
lime rock ; it is very abundant in the Plymouth Sound and in 
Torbay. 
Genus 7. SAXICAVA. 
Saxicava, Lamarck. 
Bissomie, Cuvier. 
Pholeobia, Leach. 
The shell equivalve, oblong, entire, short anteriorly, gaping 
behind ; the umbones simple, situated rather anteriorly ; the 
ligament hinge-shaped external; the hinge without teeth ; 
the valves behind the hinge ligament united by a membrane. 
The respiratory tubes of the animal are moderately and un- 
equally long, united to each other and ciliated at their extre- 
mities ; the foot very much elongated and very narrow. 
1. SAXICAVA RUGOSA. 
Shells rugose, antiquated, rounded anteriorly and posteriorly, 
and concentrically striated. Length of the shell two inches ; 
height one inch. 
Mytilus rugosus, Linn. Syst. Nat. xi. 1156; Penn. Brit. 
Zool. iv. 110. t. Ixv. f. 72; Mont. Test. Brit. 164; M. & 
R. Trans. Linn. Soc. vii. 105 ; Flem. Edinb. Encycel. vii. 
99; Dill. Desc. Cat. 304; Turt. Conch. Dict. 113. 
Saxicava rugosa, Lam. Hist. Nat. des Anim. sans Vert.v. 501. 
The mantle within the valves saffron-coloured ; the tracheal 
tubes clay-coloured, margined with pale violet, their extremities 
crimson. 
Inhabits the European ocean ; is found on most of our coasts 
burrowing in limestone or concealing itself amongst the roots 
of Fucus digitatus, or other marine plants. 
2. SAXICAVA PHOLADIS. 
Shells pale fuscous, oblong, antiquated, transversely rugose, 
rounded behind. Length of the shell one inch and a half. 
