MYTILID^. 263 



States, Europe, Thibet, South India. M. barbata, Linn, (cxxviii, 

 94). 31. ^^<Z^^a, Linn. ( cxxviii, 95). 



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 Modiolse are distinguished from the mussels by their habit 

 of burrowing, or spinning a nest, using stones, fragments of 

 shells and the byssal threads. The common American species, 

 M. plicatula, however, adheres by its byssus in masses like 

 Mytilus. !^ow- water — 100 fathoms. 



BRACHYDONTES, Swainsou, 1840. Shell radiately ribbed, car- 

 dinal margin angular and sometimes crenulated. M. plicatula, 

 Lam. (cxxviii, 96). 



ADULA, H. and A. Adams, 1855. Shell elongated, C3dindrical, 

 posterior margin obliquely truncated ; beaks submedian. M. 

 Soleniformis, d'Orbigny (cxxix, 12). 



MODiELLA, Hall, 1883. Subrhomboidal, narrowed and auricu- 

 late in front, broadly expanding posteriorly ; two well-marked 

 muscular impressions, connected by a simple pallial line ; surface 

 with radiating striae. M. pigmsea, Conrad. Hamilton Gr., N. Y. 



LiTHODOMUs, Cuvier, 181 Y. 



Syn. — Lithophaga, Bolten, H. and A. Adams. L. caudigerus 

 Lam. (cxxviii, 9t). L. lithophaga, Linn, (cxxviii, 98). 



Distr. — 40 sp. West Indies — New Zealand. Fossil, 35 sp. 

 Carb. — ; Europe, United States. 



Shell cylindrical, inflated in front, wedge-shaped behind • 

 epidermis thick and dark ; interior nacreous. 



These mollusks, when young, suspend themselves to rocks by 

 a byssus, but when adult they form cavities corresponding to 

 the shape of their shells in soft rocks or other shells. L. dactylus 

 is sold by the Mediterranean fishermen as an article of food and 

 is highly esteemed. Like other burrowing shell-fish, they are 

 luminous. Perforations of Lithodomi, in limestone cliffs and 

 in the columns of the Temple of Serapis at Puteoli, haA'^e 

 afforded conclusive evidence of changes in the level of sea-coasts 

 in modern times. 



BOTULA, Morch. Shell oblong, subrhomboidal, subcylindrieal • 

 beaks distant, subterminal. L. splendida, Dunker (cxxix, 16), 



LEiosoLENUS, Carpenter, 1856. The cavity or burrow formed 

 by the animal with the aperture prolonged into a tube, more or 

 less bilobed at the outer end, contracted at the junction. L. 

 spatiosa. Carpenter. 



