GUELPH FAUNA IN THE STATE OF NEW YORK 85 



slight curvature and traces of the longitudinal surface ornament. This 

 specimen shows a marked gerontic character in the uniformly closer 

 arrangement of the last septa and therefore furnishes an indication of the 

 mature size reached by this species. Its living chamber has a diameter of 

 48 mm and a length of 51 mm. The aperture is partly preserved and 

 appears to have been slightly curved. The chambers show the same depth 

 (about 5 mm) as in Billings's type specimen of Orth. darwini, the 

 conchs of both having a like width. The sutures have a broad, low saddle 

 on the concave side. While two of the smaller specimens bear only uniform 

 longitudinal ridges, the larger conch is provided with low annulations 

 throughout its entire length. In the best preserved young specimens from 

 the Rochester Guelph these annulations appear only in the earlier stages, 

 and it thus appears that the large individual preserved this infantile charac- 

 ter into the ephebic stage. The three factors of the surface ornamentation 

 follow evidently in the same order as observed by Clarke in annulated and 

 lineated Trenton forms and above referred to, viz longitudinal ribs, annula- 

 tions, transverse striae, but with this difference, that the annulations here 

 never attain any strong development and soon disappear, while the longi- 

 tudinal ribs appear to persist throughout life and become in the ephebic 

 stage complicated with the concentric lineation, which, however, does not 

 attain such prominence as in the mature stage of Dawsonoceras 

 annulatum or in the Trenton forms mentioned. 



Dr Whiteaves gave the first illustration of the original of K. darwini 

 and points out its identity with Hall & Whitfield's Cyrtoceras myrice 

 described at a later date from the dolomites at Yellow Springs O. Billings's 

 original was from the Guelph at Hespeler, and other specimens originally 

 identified by Dr Whiteaves with Cyrtoc. myrice are from Durham. 

 This species is, hence, to be considered a typical Guelph form. Its connec- 

 tion with the longitudinally ribbed or cancelated, slender orthoceratites, so 

 common in the Racine beds whence it probably descended, is very close, 

 specially with Orthoceras angulatum (Wahlenberg) Hall, 1 which is 



1 N. Y. State Cab. 2oth An. Rep't. 1867. p. 353. 



