GUELPH FAUNA IN THE STATE OF NEW YORK 6 1 



whorls. Near the aperture the last whorl is distinctly free from the preced- 

 ing. Aperture circular, not thickened ; umbilicus round and deep. Surface 

 bearing a series of about 20 fine, elevated, flat topped and continuous ridges, 

 of which about 15 are on the outer and upper slope of the whorl. These 

 are separated, except near the suture, by flat grooves of subequal size and 

 wider than the ridges. 



The excavated slope to the suture occupies the width of two or three 

 of these intervals, and on this faint traces of the revolving lines may some- 

 times be observed. On the umbilical surface the revolving ridges are more 

 prominent than elsewhere and more widely separated. At times these 

 ridges appear to be faintly grooved at their summits. All these ridges are 

 crossed by fine, imbricating or tilelike, concentric striae which are caught 

 back at the summits and are most sharply evident in the intervening fur- 

 rows. These lines are specially noticeable over the sutural slope where 

 they are faintly festooned by the obsolete revolving lines, and again toward 

 the umbilicus. At the aperture of adult shells they are closely crowded. 



Dimensions. A typical example of the species measures as follows : 

 hight (apex to lower margin of aperture) 28 mm; basal diameter 31 mm, 

 i. e. a ratio in these dimensions of nearly 1:1. Another example has a 

 hight of 20 mm, basal diameter of 35, a ratio of 4:7, indicating a very 

 depressed spire. 



Observations. This beautiful species is the most common of all the 

 gastropods of the Rochester fauna, and also occurs in the upper horizon at 

 Shelby, but has not been found in the lower bed. All the specimens 

 before us indicate remarkable uniformity except in the degree of elevation 

 of the spire. The species is probably related to the shell Whiteaves has 

 identified with Euomphalus (1884), 1 Polytropis (1895) macrol i n- 

 eatus Whitfield, from the Guelph at Elora and Durham, Ont., but differs 

 therefrom in proportions of the whorls, depth of suture and apparently in 

 the character of the ridges of the surface. While we are unable to find 

 closer agreement in the Canadian and New York species, we are disposed 



1 Op. cit. v. 3, pt 1, pi. 3, fig. 6. 



