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288 Superjamily PYRAMIDELLACEA Family PYRAMIDELLIDAE This is a well-known family of very small gastropods which are ex- tremely baffling to novices attempting to identify any one of the several hun- dred so-called species. Even among the experts there is not always agreement on what constitutes a species, subgenus or genus in this group. It would be impossible to present in a book this siz^e even an account of only the most common species. Those interested in delving into this interesting maze of species are referred to the works of Bartsch, W. H. Dall and K. Bush. The recent work of Fretter and Graham has shown that the Pyrams are ectoparasites, with each species feeding on a particular host, usually a tubico- lous polychaete worm or a bivalve mollusk. The Pyrams attach themselves

ATLANTIC COAST PYRA.MIDELLIDAE (Figure 62) (The names in parentheses are subgenera. Illustrations are from P. Bartsch, 1909, Proc. Boston Soc. Nat. Hist., vol. 34, no. 4. The measurements refer to the length of an average specimen). a, Odostojjiia (Chrysallida) ivillisi Bartsch. Willis' Odostome. 3 mm.; milky white. Prince Edward Island, Canada. Uncommon. b, Turbonilla (Pyrgisais) internipta Totten. Interrupted Turbonille. 6 mm.; pale waxy yellow. Casco Bay, Maine, to the West Indies. 2 to 107 fathoms. Common. c, Turbonilla (Tiirbo?iilla) stricta Verrill. Varied Turbonille. 5 mm.; milky white. Massachusetts to North Carolina. 3 to 8 fathoms. Moderately com- mon. d, Turbojiilla (Tiirbo?iilla) iiivea Stimpson. Snowy Turbonille. 5 mm.; milky white. Maine to Connecticut. 40 to 400 fathoms. Uncommon. e, Pyra7indella (Syrnola) fiisca C. B. Adams. Brown Pyram. 6 mm.; light brown. Gulf of St. Lawrence to Florida. Common. f, Odostomia (Menestho) trifida Totten. Three-lined Odostome. 4 mm.; shiny white. Maine to New Jersey. Shore. Common. g, Odostojjiia (lolaea) heiidersojii Bartsch. Henderson's Odostome. 3 mm.; glossy white. Woods Hole, Massachusetts. Uncommon. h, Odostomia (Menestho) bisutiiralis Say. Double-sutured Odostome. 5 mm.; milky white. Nova Scotia to Delaware Bay. Shore to 2 fathoms. Common. i, Odostomia (Menestho) impressa Say. Impressed Odostome. 5 mm.; milky white. Massachusetts Bay to Gulf of Mexico. Common in shallow water. j, Odostomia (Chrysallida) sejniniida C. B. Adams. Half-smooth Odostome. 4 mm.; whitish. Nova Scotia to Gulf of Mexico. Shore to 12 fathoms. Common. k, Odostomia (Odostomia) gibbosa Bush. Fat Odostome. 3 mm.; shiny, yellowish white. Maine to southern Massachusetts. Uncommon. (= modesta'^2iXX.scy not Stimpson).