CARPET-SHELL 53 
pallial sinus is very deep, and the posterior end 
of the shell is slightly gaping. 
In all the markets of San Francisco may be 
found excellent specimens of the next species, 
Tapes staminea , Conr., Carpet-shell, shown in 
Fig. 3, PI. XIV. It is known among the market 
men as the u Hard-shelled Clam.” Tomales Bay 
furnishes a good part of the supply, but it abounds 
all along the coast. The valves are rounded, 
full, strong, and marked by numerous narrow ra- 
diating ribs, which are cut by successive lines 
of growth. It has three strongly locked cardi- 
nal hinge-teeth and an external ligament ; the 
pallaial sinus reaches to the middle of the shell. 
The outside of some varieties is very prettily 
marked by reddish brown chevrons ; others are 
nearly pure white. These mollusks burrow in 
stony places, and can be dug out when the tide 
is low. Length, one to three inches. 
Fig. 5, PI. XIY, represents one of the most 
graceful of our bivalve shells, named Amiantis 
callosa , Conr., It is pure wdiite, full in the center 
but quite thin at the edges. Its sculpturing con- 
sists of many rt rinded, concentric lines, equal in 
size to the intervening grooves. There are no 
radial markings whatever. The lunule is small, 
set beneath the prominent umbones. Ligament, 
external ; pallial sinus, moderate ; hinge, with 
complicated cardinal and strong, short, lateral 
teeth. This species is found to the south, and 
sometimes is several inches long ; common length, 
two inches. 
Petricola carditoides , Conr., is a Rock-shell, 
