Raymond : Gastropoda of the Chazy Formation. 175 



Description. 



Shell simple, depressed conical, rather large, irregular in outline, 

 generally subcircular, but never smoothly curved. Apex obtuse, 

 almost central, sometimes a little back of the center. All slopes 

 about equal, generally almost straight, but occasionally a little convex. 

 Surface marked by fine lines of growth which follow the irregular 

 form of the aperture. Usually there are a few obliquely radial folds 

 and various irregular depressions and pits which do not follow any 

 symmetrical arrangement. Some of the specimens show obscure evi- 

 dences of coiling. 



The greater diameter of one specimen is 26 millimeters, lesser dia- 

 meter 25 millimeters, height 10 millimeters. The aperture of an- 

 other specimen is 19 millimeters in greater diameter, 18 millimeters 

 in lesser diameter, and 9 millimeters in height. 



Locality. — Palceacmcea irregularis is a common fossil in one zone 

 at Chazy, New York, where it is found associated with Raphistoma 

 stamineum, Lophospira rectistriata, and Scenella montrealensis. The 

 cotypes are in the Yale University Museum. 



Sub-Order RHIPIDOGLOSSA Troschel. 



Family Raphistomid^e Ulrich and Scofield. 



Genus Raphistoma Hall. 



Hall, Paleontology of New York, 1847, Vol. I, p. 28. 



Ulrich and Scofield, Paleontology of Minnesota, 1897, Vol. Ill, 

 part II, pp. 931, 940. 



Under the generic name Raphistoma, Hall described three species 

 and one variety from shells collected in the Chazy Limestone at 

 Chazy, New York. On the basis of similar specimens, which, how- 

 ever, showed a band on the outer margin of the upper surface of the 

 whorls, Billings referred all of Hall's species to the genus Pleuro- 

 tomaria., and described five new species from the Chazy of Canada. 

 Reviewing their work at the present time, with several hundred speci- 

 mens gathered from the Canadian and New York localities, it becomes 

 evident that Hall and Billings referred to the same shell under differ- 

 ent specific names. The imperfections of the material studied by 

 each led them to take different views of the characters of the shells. 

 Before stating just what synonymy has arisen from the study of this 



