Neil) or Little Knotcn j^orth American Limnctiidm. 95 



behind. It is widest immediately beneatli the tentacles. The color, 

 above, is darker than that of the body; the sole is dark bluish or lead- 

 color. The animal is sluggish in its habits, and excessiveh' timid, the 

 slightest disturbance of the water causing it to instantly draw itself 

 into the shell. Though it feeds upon algae in confinement, my speci- 

 mens also devour the animals of land snails, and of fresh water mus- 

 sels with great greediness. 



Anatomy. — The Digestive System. 



The buccal mass, fig. 1, is oblong-oval, of a bluish or lead-color, 

 :ind lies before the e^'es and between the tentacles, in a cavity of 



Fig. 1 

 B, buccal mass ; 0, oesophagus ; S, salivary glands ; S G, stomato gastric ganglion ; D, duct 

 of salivary gland; G, gizzard; P, pyloras ; I, intestine ; L, liver. 



the cephalic part of the rostrum. It is composed of dense muscular 

 tissue, containing the protractors and retractors of the radula, and also 

 a set of muscles so arranged as to vibrate the lateral jaws. It opens 

 anteriorly b}- the oval aperture which is armed with an upper and 

 two lateral jaws, and posteriorly into the oesophagus, which is long, 

 nearh' straight, and passes into the lower anterior side of the distinctly 

 bilobed stomach, at the central line. The salivary glands are white, 

 ramose, and are situated upon the oesophagus, just posteriorly to the 

 nerve collar, and open into the dorsal side of the buccal mass by two 

 long ducts which pass through the nerve collar: these ducts are bifid 

 near the glands, but the branches soon unite. The stomach or crop 

 is composed of two dense subglobular masses, made up of muscle with 

 distinctl}' striated fibres, the walls being of immense thickness and firm- 

 ness; the inside is lined with a wrinkled and dense mucous tissue, and 

 contained in the specimens dissected, a large number of small grains 

 of quartz sand. 



The pyloric poi-tion of the stomach opens on the upper posterior cen- 

 tral line, between the two muscular lobes, and gradually tapers to the 

 intestine proper, w^hich is first folded around the left side, and the 

 front of the stomach over the oesophagus, then back spirally to the 

 posterior portion of the liver, where it is flexed on itself, and passes 



