422 MARINE INVERTEBRATES 
valve, and their most prominent feature is the hinge, which is 
beset with sharp, comb-like teeth in two straight rows, one upon 
each side of a central pit, a space reserved for the ligament. 
Genus Nucula 
N. proxima. The commonest of several species of the genus found 
along the New England coast. It is oblique, with a light-olive epider- 
mis, nacreous interior, and finely crenulated margins. Its length 
is about one quarter of an inch. ‘The animal has no siphons. 
, It lives in either muddy or pebbly stations near the shore, and 
probably exists in countless thousands in all the bays and har- 
procima, bors of the New England coast. 
Genus Leda 
E. tenuisutcata. This species has a longer shell 
than the preceding; it is more produced behind, 
and is narrowed into a blunt, slightly gaping point. 
The epidermis is light greenish, and the shell has 
a pearly luster within. The outer surface of the 
shell is concentrically grooved; the beaks are 
smooth. The foot is disk-shaped, and the animal 
is provided with small siphons. The length of 
this shell is about one inch. Its station is the muddy es 
bottom in shoal water on the New England coast. Leda tenuisulcata, 
Grnus Yoldia 
Y. limatula. This species: has the same sort of toothed hinge exhib- 
ited in the two preceding species, but the shell is considerably larger 
(two inches), with a smooth 
greenish glazed epidermis. 
The beaks are nearly central. 
The interior of the shell is 
light bluish and pearly. The 
animal has two slender, short, 
united siphons and a disk- 
shaped foot with simple mar- 
gins. This species can make 
excellent use of its foot, for 
it crawls with rapidity, and 
also can execute leaps in an astonishing manner. Found in muddy 
stations in shoal water on the New England coast. 
Y. thraciceformis. A much larger species, found on the New England 
coast.. It may be distinguished by a rib-like wave extending obliquely 
from the umbones to the ventral margin of the shell, It measures over 
Yoldia limatula. 
