286 PALUDINIDiE. 



Trochus occidentalis. 



Shell pale, imperforate ; whorls seven, convex ; carhia3 light brown, smooth 

 above ; suture impressed ; columella callous. 



Trochus occidentalis, Migiiels and Adams, Best, Journ. iv. 47, pi. 4, fig. 16 (1842). 



Stimpson, Check Lists, 4. 

 Margarita alahastrum, Beck, &c. 



Shell rather small, somewhat solid, sub-translucent, pale horn 

 color, with light brown revolving caringe, of which there are three 

 on the upper whorls, and four to six on the lower one ; 

 '"■ ■ whorls seven, convex ; suture distinct ; spire three fifths 

 the length of the shell ; apex acute ; last wliorl with a 

 smooth space between the carinas and two or three coarse 

 revolving striae around the umbilical region ; aperture mod- 

 ^' "ms'"^' ei'ately depressed, transversely ovate ; labrum crcnulated 

 by the carinae ; columella callous ; umbilical region in- 

 dented. Height, five tenths of an inch ; greatest basal diameter, 

 forty-three hundredths of an inch ; divergence, sixty degrees. 



Casco Bay, taken from stomachs of haddock, in the summer of 

 1840, and subsequently {^Migiiels and Adams}. 



Family PALUDINID^, Risso.* 



Shell conical or sub-discoidal, the margins of the aperture united 

 posteriorly ; operculated ; inhabiting fresh water. 



Genus VALVATA, Muller. 1774. 



Shell conical, whorls cylindrical, loosely cohering ; aperture cir- 

 cular, its margin entire ; operculum orbicular. 



Valvata tricarinata. 



Fig. 156. 



Shell sub-discoidal, thin, pale pea-green ; whorls three, the last tri-carinate ; 

 umbilicus large. 



Cuclostoma tricarinata, Sat, J. Acad. N. S. Piiil. i. 13, 1817; Nich. Encyc. ed. 3; BiN- 

 ney's ed. 68, .59, 56. 



* In prcparinn: this family I have larfjely borrowed from the " Land and Fresh-water 

 Shells of North America," Part III. Professor Henry has allowed the use of some of the 

 woodcuts prepared for that work. — W. G. B. 



