454 MOLLUSCA. 
length, when the upper margin rounds downwards; posterior extre- 
mity broadly rounded; epidermis glossy, first triangular third of a 
scorched, dark chestnut-brown or tar-colour, palest at extremity ; pos- 
terior third pale ‘yellowish horn-colour; behind the umbonal ridge 
rigid with a coating of the loose fringe-like terminations of the layers 
of growth; interior pearly white; slightly gaping in front. 
Diameters: longitudinal, four inches; vertical, an inch and three- 
quarters; transverse, an inch and a quarter. 
Inhabits Oregon; Puget Sound, Townsend Harbour, California. 
A very well-marked species, more than usually cuneate, and with 
the beaks quite remote from the summit. 
An old specimen from San Francisco is much more elongate, fal- 
cate, not dilated vertically so much. A young specimen from the 
Gulf of California is almost lanceolate posteriorly, and compressed 
laterally. All agree in the anterior extremity, in tissue, colour, &c. 
Figures 561, 561 a, lateral and dorsal views of the shell. 
Myritus (Modiola) nepaticus (Gould). 
T. parva, elongata, ovato-triangularis, antice angustata, ventricosa ; 
margine dorsali angulato; apicibus acutis, angulatis ; epidermade 
tenut, livido-corneo, versus fastigium umbonalem flavescente: intus 
punicea, luteo-marginata. 
Mytilus (Modiola) hepaticus, Goutp; Proceed. Boston Soc. Nat. 
Hist., 11. 343. Dec. 1850. Expedition Shells, 93. 
SHELL small, elongated oval, dorsal edge angular at the middle, 
upper portion rectilinear ; lower slightly curved, nearly parallel with the 
base, narrow and rounded at tip; beaks acute, near the end; umbonal 
slope angular; dorsal portion compressed; ventral margin incurved 
at centre, to which a slight radiating constriction of the valves is di- 
rected ; byssal opening very narrow ; epidermis bluish-green, glaucous 
on the disk, chestnut on the belly, loosely laminated and produced 
