222 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Interior whitish, not polished. When fresh all organs are represented 
in a faint impression on the inner surface, but this becomes obscure when 
the shell is contracted by drying. Internal laminse prominent. In all 
the specimens of this genus which I have seen the right lamina in the 
neutral valve is a little longer than the other. 
The muscles are attached on the inner concave edges of the laminae. 
The muscular impressions are very small and obscure. Length of shell, 
1.7 inches; greatest width, 0.55 inches. Length of peduncle, 4.5 inches. 
(Dali.) 
Type in U. S. N. M. Type locality, head of Gulf of California. 
Range. San Pedro, California, to head of Gulf of California. 
Genus DISCINISCA Dali, 1871. 
Lower valve more or less flattened, concave or compressed, upper valve 
more convex; apices of both subcentral or subposterior; lower valve with 
a small septum, as in Discina , behind which is a disk or area impressed 
from the outside, and traversed by a longitudinal fissure in the median line 
of the valve; shell more or less horny in texture, minutely tubulous. (Dali.) 
Distribution. West coast of North and South America, Japan, 
China, Nicaragua, Brazil, Jamaica, Philippines. Fossil, Silurian to recent. 
Type. Discinisca lamellosa Broderip. 
Discinisca strigata Broderip, 1833. 
Plate 49, figs. 4, 5. 
Trans. Zool. Soc., 1:143; pi. 23, fig. 1. 
Orb. testa crassiuscula, subrotunda, substriata, radiatim castaneo stri¬ 
gata ; epidermide tenui, fusca. Long., % 2 i lat., vix % 2 1 crass., % 2 poll. 
(Broderip.) 
Mr. Cuming dredged two individuals of this species at the depth of 18 
fathoms. They were attached to rocks. The dimensions are taken from 
the largest specimen; but the smallest is figured on account of the superior 
brilliancy of the stripes. (Broderip.) 
Type in Museum Cuming. Type locality, Cana Island, Guatemala, 18 
fathoms. 
Range. San Pedro, California, to Margarita Bay, Lower California; 
Mazatlan; Nicaragua; Panama. 
Family RHYNCHONELLID2E. 
Genus HEMITHYRIS Orbigny. 
Pal. Franc. Ter. Cret. y 4:342, 1847. 
Shell trigonal, acutely beaked, usually plaited; dorsal valve elevated in 
front, depressed at the sides; ventral valve flattened, or hollowed along 
