CONCHIFEUA. 421 



known cause they are at times extremely deleterious. The 

 consumption of mussels in Edinburgh 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. J^t Port Stanley, Falkland Islands, 

 Mr. Macgillivray noticed beds of mussels which were chiefly 

 dead, being fi'ozen at low-water. M. hilociUaris (Septifer, 

 Eecluz) 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, Eussian Ice-meer; Black Sea, Cape Horn, Cape, New 

 Zealand. 



. Fossil, 100 species. Silurian — . United States, Europe, 

 South India. 



? Myalika, 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 Area ohliquata, 

 Chemn. India. 



Modiola, Lam. Horse -mussel. 



Etyr^iology , modiolus, a small measure, or drinking- vessel. 



Example, M. tulipa, PI. XVIL, 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 ModiolcB are distinguished from the Mussels by their 

 habit of burrowing, or spinning a nest. Low water — 100 

 fathoms. 



