MYTILIDA. 263 
States, Europe, Thibet, South India. JL barbata, Linn. (cxxviii, 
94). MM. tulipa, Linn. (exxviii, 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 Modiole 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. Low-water—100 fathoms. 
BRACHYDONTES, Swainson, 1840. Shell radiately ribbed, car- 
dinal margin angular and sometimes crenulated. MM. plicatula, 
Lam. (cxxviii, 96). 
ADULA, H. and A. Adams, 185). Shell elongated, cylindrical, 
posterior margin obliquely truncated; beaks submedian. J. 
Soleniformis, d’Orbigny (cxxix, 12). 
MODIELLA, Hall, 1888. 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. pigmea, Conrad. Hamilton Gr., N. Y. 
Lituopomus, Cuvier, 1817. 
Syn.—Lithophaga, Bolten, H.and A. Adams. JZ. caudigerus, 
Lam. (exxviii, 97). L. lithophaga, Linn. (exxviii, 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. Z, 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, have 
afforded conclusive evidence of changes in the level of sea-coasts 
in modern times. : 
BoTuLA, Mérch. Shell oblong, subrhomboidal, subeylindrical ; 
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. JZ. 
spatiosa, Carpenter. 
