56 
CALIFORNIA SEA SHELLS. 
back of the umbo. The hinge teeth are very 
small, and the pallial sinus extends nearly the 
whole length of the shell. Behind the ligament, 
the shell narrows into a short, brownish wing. 
The length varies from two to four inches. 
Macoma nasuta , Conr., PI. XV, Fig. 3, is a 
very common species, reaching from Kamtschatka 
to Mexico. It is abundant in San Francisco Bay, 
and some of the large shell-mounds of the aborig- 
ines, on the shores of that bay, are largely com- 
posed of the valves of this species. It inhabits 
muddy flats, burrowing quite deeply, and 
reaches the water by its two, small, red siphons. 
The shell is smooth and thin ; the posterior part 
is narrowed and twisted to one side. The hinge 
teeth are small, thejigament is external, and the 
pallial sinus reaches to the forward muscular 
scar. The common length is two inches. 
The Red-lined Sand-shell, Psammobia rubro- 
radiata , Nutt., is a fine shell, represented in Fig. 
4, PI. XV. The figure was drawn from a shell 
found at Monterey, which measures two and one 
half inches in length. The outside of the shell 
is smooth and whitish, marked with broad, radi- 
ating, red bands, much resembling the rays of 
the setting sun. The inside is of a fine, glossy 
white, like choice porcelain. Hinge teeth, small ; 
ligament, external ; sinus, large. 
Sanguinolaria Nuttallii, Conr., is a southern 
species. The shell is thin, rounded and flatten- 
ed, covered with a glossy, dark brown epidermis, 
beneath which may be seen radiating bands ’of 
color. Ligament, large and external; pallial 
sinus, very large ; length, three inches. 
