GUELPH FAUNA IN THE STATE OF NEW YORK 



87 



Cyrtoceras arcticameratum Hall 



Plate 15, fig. i, a; plate 16, fig. 1-7 



Cyrtoceras arcticameratum Hall, Paleontology of New York. 1852. 2:349, 



pi. 84, fig. 7a-d 

 Cyrtoceras arcticameratum Billings, in Logan's Geology of Canada. 1863. 



P- 34° 

 Cyrtoceras arcticameratum Whiteaves, Paleozoic Fossils. 1895. v. 3, pt 2, 

 p. 103 



This species was very briefly characterized by Hall in the following 

 words : " Elongated, slender, gradually tapering and gently incurved ; septa 

 numerous ; slightly convex ; section transversely oval, siphuncle dorsal." 

 The original specimens from Gait were not very good. Billings cites Gait 

 and Hespeler as localities, but Whiteaves states that he has seen no speci- 

 mens of the species. It has also been recognized in the Guelph at Cedar 

 burg Wis. 1 



In the Rochester material there are several examples, one of excellent 

 quality, which present characters agreeing with Hall's diagnosis and figures, 

 and these are specially marked by their long, slender and gently arcuate 

 cones, in which the outer ventral curve is about 87 and the inner 69 . The 

 section is nearly circular in early growth but later becomes broadly oval. 



The living chamber is long, somewhat swollen in the middle, broadly 

 contracting to the aperture, which has straight lateral margins. Septa 

 from 2 to 3 mm apart, slightly concave and nearly transverse, broadly 

 flexed forward ventrally. Siphuncle small and ventral. 



Surface smooth, only fine concentric lines being visible. These become 

 squamous toward the aperture and all recurve ventrally at the hyponomic 



sinus. 



Dimensions. The most complete of these examples has a length meas- 

 ured on the outer curve of 95 mm. This covers most of the living chamber, 

 which is 29 mm long. Width of living chamber dorsoventrally 21 mm, of 



aperture 1 6 mm, of lower end of specimen 9 mm 



'Geol. Wisconsin, 2:380. 



