CONCHIFERA. 421 
known cause they are at times extremely deleterious. The 
consumption of mussels in Hdinburgh and Leith is estimated 
at 400 bushels (— 400,000 mussels) annually ; enormous quan- 
tities are also used for bait, especially in the deep sea fishery, 
for which purpose thirty or forty millions are collected yearly 
in the Firth of Forth alone. (Dr. Knapp.) Mussels produce 
small and inferior pearls. At Port Stanley, Falkland Islands, 
Mr. Macgillivray noticed beds of mussels which were chiefly 
dead, being frozen at low-water. WM. bilocularis (Septifer, 
Recluz) has an umbonal shelf for the support of the anterior 
adductor, like Dreissena ; it is found at Mauritius and Australia. 
M. exustus (Brachydontes, Sw.) has the hinge-margin denti- 
culated continuously. 
Distribution, 65 species. World-wide. Ochotsk, Behring’s 
Sea, Russian Ice-meer; Black Sea, Cape Horn, Cape, New 
Zealand. 
Fossil, 100 species. Silurian —. United States, Europe, 
South India. 
? Myauina, Koninck, 1842. 
Types, M. Goldfussiana, Kon. Carb. M. acuminata, Sby. 
Permian. 
Shell equivalve, mytili-form ; beaks nearly terminal, septi- 
ferous internally; hinge-margin thickened, flat, with several 
longitudinal cartilage-grooves; muscular impressions two; 
pallial line simple. 
Fossil, 6 species. Carb. — Permian. Europe. The liga- 
mental area resembles that of the recent Arca obliquata, 
Chemn. India. 
Mopto1LA, Lam. MHorse-mussel. 
Etymology, modiolus, a small measure, or drinking-vessel. 
Example, M. tulipa, Pl. XVII., Fig.5. M. modiolus, p. 403, 
Fig. 214. 
Shell oblong, inflated in front; umbones anterior, obtuse; 
hinge toothless; pedal impressions three in each valve, the 
central elongated ; epidermis often produced into long beard- 
like fringes. 
Animal with the mantle-margin simple, protruding in the 
branchial region; byssus ample, fine; palpi triangular, pointed. 
The Modiole are distinguished from the Mussels by their 
habit of burrowing, or spinning a nest. Low water—100 
fathoms. 
