286 PALUDINID^. 



Trochus occidentalis. 



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

 above; suture impressed ; columella callous. 



Trochus occidentalis, Mighels and Adams, Best. Journ. iv. 47, pi. 4, %. 16 (1842).— 



Stimpson, Cliec'k 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 whorl with a 

 smooth space between the carina) and two or three coarse 

 revolving strise around the umbilical region ; aperture mod- 

 erately depressed, transversely ovate ; labrum crenulated 

 by the carinas ; 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 {^Miglicls and Adams). 



Family PALUDINID^, Risso.* 



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

 posteriorly ; operculated ; inhabiting fresh water. 



Oeniis VALrVATA, Mijller. 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. 



Ci/clostoma tricarinata, Say, J. Acad. N. S. Pliil. i. 13, 1817 ; Nich. Encyc ed. 3; Bin- 

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



* Tn preparing this family I have largely borrowed from the " Land and Fresh-water 

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

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



