54 



RANDOM NOTES ON NATURAL HISTORY. 



The Shell-Bearing Mollusca of Rhode 

 Island. 



BY HORACE F. CARPENTER. 



Chapter XVIII. 



The Cerithiidae farail\', or Cerites, are a 

 very numerous group of turreted shells, with 

 a notch or canal in front. They are found 

 in all parts of the world, but the typical 

 species are tropical in their distribution. 

 They inhabit salt, brackish, and fresh water 

 The genus Potamides, Brong, or fresh water 

 Cerites, numbering about Mty species, are 

 all tropical or sub-tropical, living in fresh 

 and brackish water (streams and swamps). 

 The genus Cerithium, Brug, contains about 

 one hundred and forty species, distributed 

 among thirteen sub-genera, two of which, 

 Bittium and Cerithiopsis, are represented 

 in Rhode Island, each bv two species. 



49. Cerithium (Bittium) nigrum, Stimpson. 



Syns. : 



Cerithium reticulatum, Totten, Am. Jour. 

 Sci., xxviii., 352. 



Pasithea nigra, Totten, Am. Jour. Sci., 

 XXVI., 369. 



Cerithium Sayi, Menke, Gould, DeKa}', 

 Stimp. 



Dist., Mass. Bay to South Carolina. 



Shell small, turreted, whorls six to eight, 

 the upper ones of a dark bluish or blackish 

 color, the lower ones of an ashy gray ; sur- 

 face covered with about twenty ribs, reticu- 

 lated by revolving lines, of which there are 

 six on the second whorl, five on the next 

 above, and so on ; on the body whorl the 

 net work extends downward to the centre ; 

 below this are six revolving lines, without 

 the ribs ; aperture one-fourth the length of 

 the shell ; outer lip sharp, scalloped bj' the 

 revolving lines ; canal a mere fissure ; shell 

 umbilicated. Length three-tenths, breadth 

 one-tenth inch. The 3'oung of this species 

 are found verj' abundantly on the sand be- 

 tween tides at Nantucket, Martha's Vine- 

 3'ard, New Bedford, Narragansett Bay, and 

 Long Island Sound. These are always red- 

 dish black and have a round aperture, or 



nearly so. The adults are found from low 

 water to eight fathoms on algae and eel grass. 

 They attain their growth in two or three 

 years, and when full grown have an oblique 

 aperture, flaring at the base and suddenly 

 everted. 



50. Cerithium (Bittium) Greenii, Adams. 



Shell small, reddish black (resembling 

 veiy closel3- the young of the preceding 

 species), elevateti-conic, whorls ten to 

 twelve, flattened, traversed hy numerous 

 ribs, of which there are on the bod}' whorl, 

 from twent3'to twent\'-five, crossed b^' three 

 revolving lines, producing three sets of 

 granules, the lower one the largest, so that 

 the base of each whorl appears to jut over 

 the other ; as these lines revolve up the 

 spire, the lower one disappears, then the 

 middle one, and finalh' the last one vanishes, 

 leaving the upper part of the shell near the 

 apex quite smooth ; two black threads 

 emerge from the aperture and revolve around 

 the base of the shell ; aperture one-eighth 

 the length of the shell, nearly circular, with 

 a deep but short canal, parth' closed over 

 b}' the lips. Length one-fifth of an inch, 

 breadth one-twentieth. Found b}' Prof. C. 

 B. Adams on seaweed in Dartmouth Harbor, 

 a few feet below low water mark, and 

 described by him in the Jour. Bost. Soc. 

 Nat. Hist., II., 287. It inhabits the same 

 localities as nigrum, but is not at all com- 

 mon in Rhode Island. Very rare at New 

 Haven (Perkins). Boston Harbor (Stimp- 

 son). Long Island (S. Smith). Fort Ma- 

 con, N. C. (Coues). 



51. Cerithium (Cerithiopsis) Emersonii, 



Adams. 



Shell small, conical, gloss}', reddish-brown ; 

 whorls sixteen or seventeen, flat, each with 

 three rows of granules ; suture deeply 

 impressed ; aperture small, one-sixth the 

 length of the shell, with a sliort, twisted 

 canal ; outer lip crenulated. Length one- 

 half inch, breadth one-eighth. 



Discovered at Nantucket, and in New 

 Bedford harbor, by Prof. C. B. Adams, and 

 described in the Jour. Bost. Sor. Nat. Hist., 

 II,, 284, under the name of Cerithium Emer- 

 sonii, in honor of the president of the 

 societ}', Mr. G. B. Emerson. Huntington 

 and Greenport, Long Island (S. Smith). 



