GUELPH FAUNA IN THE STATE OF NEW YORK 



99 



phragmoceeas Sowerby 

 Phragmoceras parvum Hall & Whitfield 



Plate 21, fig. i-8 



Phragmoceras parvum Hall & Whitfield, Paleontology of Ohio. 1875. 2: I S I > 



pi. 8, fig. 10 

 Phragmoceras parvum Whiteaves, Paleozoic Fossils. 1884. v - 3» pt 1, p. 41, 



pi. 7, fig. 2 

 Phragmoceras parvum Arey, Rochester Acad. Sci. Proc. 1892. 2:107 

 Phragmoceras parvum Whiteaves, Paleozoic Fossils. 1895. v. 3, pt 2, p. 105 



Of the several species of Phragmoceras which have been described by 

 various authors from American Upper Siluric faunas one, P. parvum, is 

 notable for its small size and the projection of the dorsal horn of the aper- 

 ture. This species has been described only from internal casts of the 

 chamber of habitation. The original is from the dolomites at Cedarville, 

 Greene co. O., and others identified therewith are from the Guelph at 

 Hespeler. There are before us several fine small examples of Phragmo- 

 ceras from Rochester which retain in exceptional perfection the exterior 

 surface, the form of the apertural and septate portions, features which for 

 the most part have not been made known of P. parvum. 



These shells in their entire condition are unguiform, sloping from a 

 stout chamber of habitation by a gentle curve to an acute apex, the septate 

 portion making about one half the length of the shell. The section of the 

 living chamber is broadly oval, but on the earlier parts the cone is more 

 flattened on the sides. The ventral margin is very broad, the dorsal 

 narrowly rounded and subangular. In expanding upward, the shell becomes 

 rather abruptly swollen at the base of the body chamber, thence, at first 

 gradually, then abruptly, contracting to the aperture, where two lateral 

 flanges of the shell almost meet in a median line, leaving a slitlike opening 

 between. The surface of this almost plane and vertically deflected area 

 slopes upward to the ventrolateral angle, where it is somewhat produced in 

 the form of a rather blunt tube. At the dorsolateral angle the tube is 



