SAXICAVIDA. 135 
.SAXICAVA, Bellevue, 1802. 
Htym.—Saxum, stone ; cavo, to excavate. 
Syn.—Byssomya, Cuv., 1817. Rhomboides, Bl. Hiatella, 
(minuta), Daud., 1799. Biapholius, Leach. Arcinella (carinata , 
Phil. - Clotho, Faujas Saint-Fond, 1807, 
Distr.—12 sp. Universal. Fossil; Jurassic, Cret. ? Tert.—. 
Shell when young symmetrical, with two minute teeth in each 
valve; adult rugose, toothless ; oblong, equivalve, gaping, liga- 
ment external; pallial line sinuated, not continuous. 
Animal with mantle-lobes united and thickened in front; 
siphons large, united nearly to their ends, orifices fringed ; pedal 
opening small, foot finger-like, with a byssal groove; palpi small, 
free; gills narrow, unequal, united behind and prolonged into 
the branchial siphon. 
Five genera and fifteen species have been manufactured out of 
varieties and conditions of the Protean 8. rugosa, Linn. (cv, 91, 
92). It is found in crevices of rocks and corals, and amongst 
the roots of sea-weed, or burrowing in limestone and shells; at 
Harwich (England) it bores in the cement stone (clay iron-stone), 
at Folkestone in the Kentishrag,and the Portland stone employed 
in the Plymouth Breakwater has been much wasted by it. Its 
crypts are sometimes six inches deep (Couch); they are not 
quite symmetrical, and like those of the Lithodomus, are inclined 
at various angles, so as to invade one another, the last comers 
cutting quite through their neighbors ; they are usually fixed by 
the byssus to a small projection from the side of the cell. The 
Saxicava ranges from low-water to 140 fathoms; it is found in 
the Arctic seas, where it attains its largest size; in the Mediter- 
ranean, at the Canaries, and the Cape. It occurs fossil in the 
Miocene tertiary of Europe and in the United States, and in all 
the glacial deposits. 
Sometimes they do considerable damage to sea-walls. In the 
young state, Saxicava rugosa gapes at the superior margin, and 
the hinge is composed of a small tooth in the right valve, and 
two rather larger oblique teeth in the left valve; in this condi- 
tion it is the Hiatella of Daudin, and the Arcinella carinata of 
Philippi. 
“Successive generations will occupy the same hole. The last 
inhabits the space between the valves of its predecessor. In this 
way four or five pairs of shells may be frequently seen nested one 
within the other, and not unusually a Sphenia Bingham in the 
centre of all. Cailliaud observed a Saxicava within a specimen 
of Venerupis Irus, which it had perforated.”—Jkrrrreys, Brit. 
Conch. 
PARAMYA, Conrad, 1860. (Myalipa, Conrad, 1838, not Kon- 
inek.) . Shell subovate, inequilateral, ventricose over the umbonal 
slope, slightly flattened from beak to base; surface with irregular 
