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. 



JV. proxiina. 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- 

 bors of the New England coast. 



GENUS Letla 



L. tenuisulcata. 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 

 bottom in shoal water on the New England coast. 



Leda tenuisulcata. 



GENUS Toldia 



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 



Toldia limatula. 



