GASTEROPODA. 33 



Macrocheilus Hamilton^:. 



PLATE XII, FIGS. S-H. 



Macrocheilus ffamiltoniw, Hall. Descriptions of New Species of Fossils, etc., p. 21. 1861. 



" Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 49, pi. 4, fig. 2. 1862. 

 " " " Illustrations of Devonian Fossils: Gasteropoda, pi. 12. 1876. 



Shell very ventricose. Spire short, consisting of four or five volutions, the 

 last extremely ventricose, making nearly two-thirds the entire height of 

 the shell. Aperture longitudinally oval, obtuse below. Shell distinctly 

 striated by fine lines of growth; suture-line deeply impressed. Length 

 about three-fourths of an inch, with a diameter nearly as great. 



This shell resembles, in some features, the shorter and more ventricose forms 

 of this genus in the Coal measures, the spire resembling that of M. primigenius. 

 This species is almost equally rare with the preceding. 



Formation and locality. In the coarse shales of the Hamilton group at Ham- 

 ilton, Madison county, N. Y. 



Macrocheilus (Holopea) macrostomus. 



PLATE XII, FIGS. 15-18. 



Macrocheilus (Holopea) macrostomus. Hall. Descriptions of New Species of Fossils, etc., p. 21. 1861. 



" " " " Fifteenth Rep. N. Y.St. Cab. Nat. Hist., p. 49, pi. 4, fig. 3. 1862. 



" " " " Illustrations of Devonian Fossils : Gasteropoda, pi. 12. 1876. 



Shell short, subglobose. Volutions, about four or five, all above the last two 

 minute, the last one extremely ventricose, so that the width from the 

 columella is about two-thirds its height; greatest width of the shell 

 equal to the height. Aperture rounded, a little extended on the lower 

 side ; umbilicus not closed. 



Surface marked by fine equal striae of growth, Avhich are strongly directed 

 backwards from the suture. Suture-line a little depressed below the plane 

 of the convexity of the volution ; the strife sometimes crowded in fascicles. 



This species resembles in form some of the Platyostomae, but the texture of 

 the shell and surface markings are not in accordance with the well-marked 

 species of that genus. Its surface characters and general form are similar to 

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