14 NEW-YORK FAUNA — MOLLUSCA. 



SECTION 3. TECTIBRANCHIA: 



The branchice are on the back, a little inclining to the right, composed of lamina more or 

 less divided but not symmetrical, generally protected by expansions of the mantle. Gene- 

 rative organs on the same individual, but distant on the right anterior side, and connected 

 by an external furrow. They are more or less covered by a mantle, in which there is 

 generally a small shell. 



FAMILY ACERIDM. 



Animal divided into lobes or distinct parts, of which, the lateral ones dilate into expanded 

 fins. No tentacula, or at least the tentacula unite into a sort of disk in front. Branchiae 

 in a cavity on the back, somewhat posterior and a little on the right side. Shell covered 

 by the mantle, external, internal, or entirely wanting. 



GENUS BULLA. Linnaus. 



Animal oblong, obtuse at the two extremities, divided into four lobes. Head not distinct. 

 Foot expanded, bent on the right side. Genitals on the same side, distant. Shell thin, 

 oval or cylindrical, and nearly covering the animal. The last whorl enclosing all the 

 others, and rarely exhibiting any spire. Aperture long and narrow, nearly the length of 

 the shell ; lip sharp. 



Bulla insculpta. 



PLATE V. FIG. 100. a. B —(STATE COLLECTION.) 



Bulla insculpta, Totten, Am. Jour. Sc. Vol. 28, p. 350, fig. 4. 

 B. id. Gould, Invertel). Mass. p. 162, fig. 92. 



Description. Shell small, thin, fragile, pellucid, oval, impressed at the top, regularly rounded 

 and widest below, with many slight longitudinal wrinkles, a few obsolete longitudinal waves, 

 and very numerous equal impressed revolving lines. Spire none, but in its place a pit not 

 deeper than the origin of the right lip. Aperture nearly linear above, thence expanding to a 

 considerable breadth. Right lip regularly arched, sharp, rising from the axis with a regular 

 curve upwards and forwards, higher than the shoulder of the shell. Left margin, above, a 

 thin plate glued upon the convexity of the second turn ; below, rolled into a kind of spiral 

 pillar. Umbilicus none ; a very thin plate of enamel covering the inner margin. 



Color. White with a tinge of bluish. 



Length, 0- 35 -0-45. Diameter, 0' 23-0' 25. 



