and Shells of Massachusetts Bay. 69 
outer one, the interval between the two being filled with 
a colorless fluid, rendering the external coat impercepti- 
ble except upon a close examination; their form is 
slightly convex on the back and front, flattened towards 
the sides and tubular at their extremities; the foot is 
broad and fleshy at the sides, but transparent in its mid- 
dle portion, divided at its upper extremity so as to form 
a short, thick, tentaculiform appendage upon each side ; 
its width continues undiminished till near the caudal 
extremity, when it is narrowed somewhat abruptly, and 
terminates in a short point. "The genitalia are situate in 
a large tubercle upon the right side, a short distance 
behind the neck; the male organ is quite large and 
linguiform ; the excretory duct is on the same side, near 
the middle of the body, and slightly prominent. 
Eoris (Tergipes, Cuv.) GYMNOTA. 
Plate I. fig. 3. 
E. corpore elongato, albido, capite brevi, orbiculato-depresso, tenta- 
eulis quatuor, branchiis fbrcismteconiibul] utrinque fasciculis sep- 
tem, medio nem nudo. 
Length eighteen twentieths, breadth of expanded foot 
two twentieths of an inch. 
Habit. same as preceding species. 
My own collection. 
Cabinet of Bost. Soc. Nat. History. 
- Description. Body elongated, slender, tapering 
gradually from head to tail; neck very distinct; head 
short, depressed, orbicular; mouth comparatively small, 
perpendicularly linear; tentacule four, the inferior pair 
situate laterally and superiorly on the front of the head, 
smooth, round, and about an eighth of an inch long, the 
superior pair, near the middle and back of the head, 
