INSTITUTE OF SCIENCE, PHILADELPHIA. 4O5 



tions analogous to that of tiles on a roof; base with five or six strong spirals 

 of the same sort and two or three smaller ones around the umbilicus; periph- 

 ery with a single broad smooth spiral, not intersected by the transverse 

 sculpture, and on which the suture is closely laid; umbilicus small, deep, sub- 

 cylindrical, its marginating riblets forming a projection at the aperture ; 

 whorls and base slightly rounded, periphery moderately so; surface polished; 

 aperture rounded-quadrate. Alt. of shell 1 5 ; max. diam. of base 14 mm. 



The characters of this fine shell are very distinctive, and it can readily be 

 distinguished from any other of our Tertiary species. 



Oalliostoma (Eutrochus) humilis Conrad. 



Trochus humilis Conr., Journ. Acad. Nat. Sci. vi. p. 219, pi. ix. fig. 5, 1830. 

 Zizyphinus himiilis Cont., Cat. Mioc. Fos., Proc. Acad. Nat. Sci. for 1862, p. 569, 1863. 

 Trochus conus H. C. Lea, Trans. Am. Phil. Soc. ix. p. 39, pi. 37, fig. 82, 1845 (young 



specimen, from type). 

 Zizyphinus conus Conrad, Cat. Mioc. Fos., p. 569, 1863. 

 Trochus lens H. C. Lea, op. cit. p. 39, pi. 37, fig. 83, 1845 (young). 

 Zizyphinus lens Conrad, op. cil. p. 569, 1863. 

 Delphinula trochi/ormis Lea, op. cit. p. 36, pi. 36, fig. 73, 1845 ; fide Meyer, Proc. Am. 



Phil. Soc. XXV. p. 137, 1888. 

 Trochus reclusus Conrad, Journ. Acad. Nat. Sci. vi. p. 219, pi. 9, fig. 6, 1830 (probably). 

 Zizyphinus reclusus Conrad, Cat. Mioc. Fos., p. 569, 1863. 



Chesapeake Miocene of St. Mary's River, Maryland (Conrad), and 

 Petersburg, Va. (Lea). 



This species, of which the extremely young and broken tips furnished 

 Lea with several of his supposed species, verges toward Omphalius in its 

 general aspect, but does not attain the keel bordering the umbilical callus. I 

 was unable to find in the Academy's collection any specimen under the name 

 of T. reclusHS Conr. not referable to this species, and Conrad's description 

 and figure are so inadequate as to render its distinctness a matter of grave 

 doubt. 



Among the other species of Trochus in the earlier literature of our 

 Tertiaries not above referred to, T. rusticus H. C. Lea is a very young, 

 fragmentary Omphalius ; T. aratus Lea is an unrecognizable apical fragment ; 

 T. gemma Tuomey and Holmes is with little doubt the same as Liotia 

 tricarinata Stearns. I have not seen the type of T. peralveatus Conrad, 

 which, however, has been obtained by Burns at Jones's Wharf, Patuxent River, 

 Maryland, and is a very fine and distinct species. 



T. nixus Tuomey {jiexusf), from the Eocene of Wilmington, N. C, is a 

 fine species of Pleurotomaria, allied to P. Adansoniana. Trochus alabamiensis 

 Aldrich, from the Eocene of Matthews' Landing, Alabama, is referable to the 

 genus Solariella or Margarita. 



C. Guppyaniim Gabb appears to be a good species. It is from the Costa 

 Rica Pliocene. 



In the Older Miocene of Bowden are found C. decussation Gloyne, 



