GASTEROPODA. 



115 



No. 295. Pleurotomaria sulcomarginata, Con. 



The sliell of this genus, the type of a family, is distingui.shed by its sub- 

 quadrate aperture, with a slit in its outer lip; 400 species are known from the 

 Palaeozoic and Mesozoic. Hamilton Group, Onondaga Co., New York. 



No. 296. Pleurotomaria ornata, Defrance. 

 This species takes its name from the row of tubercles 



which crowns its spiral whorls. 

 Oolite of Calvados, France. 



From the Inferior 



No. 297. Pleurotomaria conoidea, Deshayes. 

 Lower Oolite, Bayeux, France. 



No. 298. Murchisonia bellicinata, Hall. 



Shell elongated, many-wliorled, and variously sculptured. The genus is 

 characteristic of the Palaeozoic; 50 species known. Family Pleurotomarid?e. 

 Cincinnati Group, Waynesville, Ohio. 



No. 299. Bellerophon bilobatus, Sow, 



In this Palaeozoic genus the shell is symmetrical, globular or discoidal, 

 whorls few, dorsally keeled, aperture notched on the dorsal side; 150 species 

 are known, all from tlie Palaeozoic. Family Bellerophontidse. Trenton period, 

 Beloit, Wisconsin. 



No. 300. Bellerophon hiulcus, Sow. 

 Carboniferous Limestone, Tournay, Belgium. 



No. 301. Maclurea Bigsbyi, Hall. 



In this singular genus of the family Macluridse (Atlantidse of old authors), 

 the shell is discoidal, and tlie spire deeply sunk. It possesses other interest- 

 ing characters. Tryon makes it the type of a distinct family. It is confined 

 to the Lower Silurian. From the Maclurea Limestone (Trenton Period), 

 Knoxville, Tenn. 



No. 302. Dentalium elephantum, Linn. 



These "tooth-shells" are placed by Huxley with the Pteropods, 

 Some authors make them a distinct class, Scaphopoda. They are 

 straight or slightly curved tubes, open at both ends and resemble 

 the cases of Annelids. They have been described from the Palaeo- 

 zoic. Quaternary Palermo, Sicily. 



No. 303. Dentalium hexagonum, Sow. 

 Tertiary, San Diego, California. 



