PAMP-SHELLES AND THEIR ALLIES 23 
Yoldia montereyénsis, Dall, the Monterey Yoldia, 
has a length of 52mm. It was dredged in Mon- 
terey Bay, from mud where the water was nearly 
half a mile deep. The hinge-teeth are about 20 
in number on each side, and the epidermis is green. 
The other Yoldias will be briefly mentioned in the 
List. It may be well to mention the fact that the 
name Yoldia is derived from that of the Countess 
Yoldi, to whom this genus was dedicated by Moller, 
im 1832. 
The genus Malletia resembles Yoldia, but the 
ligament is external, elongated, and prominent, 
while in Yoldia it is slight. Mallétia faba, Dall, 
the Bean Malletia, has an elegant little shell, 
nearly an inch long. It is smooth, ovate, inflated, 
with a polished epidermis. It has been dredged 
from deep water off the coast in various places 
from British Columbia to San Diego. 
The Arcidg, though very abundant in some 
parts of the world, are but poorly represented on 
this coast. In general they prefer warmer waters, 
being especially common on the coast of Florida. 
The Arks, as they are called, have a great number 
of small hinge-teeth, which are similar in shape, 
and taken together they resemble a comb. The 
shells are generally strong and well developed. 
Arca reticulata, Gmel., the Cross-lined Ark, is 
very small, and has been found from San Pedro 
southward. Arca mutabilis, Sby., and Arca mul- 
ticostata, Sby., are occasionally found at San Pedro 
and vicinity, though really belonging to the fauna 
of Mexico. 
