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NEW YORK STATE MUSEUM 



The development and repression of the longitudinal ridges before 

 that of the annulations already in early Beekmantown time, hence 

 near the very starting point of the whole class of Cephalopoda is an 

 interesting illustration of the principle that types are evolved more 

 quickly and changes take place more rapidly near the point of origin 

 of a stock of organisms than at any later period of their existence. 

 Smooth, fluted and annulated conchs appear in the oldest cephalo- 

 podiferous beds known to us, and the faster or slower suppression 

 of the successive stages together with the reappearance of the earliest 

 characters in reversed order in the phylogerontic condition of the 

 class supply all the variety of sculptural modification of the later 

 forms without the addition of any new essential element. 



In view of this much accelerated development of the annulated 

 cephalopods we doubt that the divisions proposed by Hyatt 

 and based on the presence or absence, continuity or discon- 

 tinuity of the longitudinal ridges can be maintained. The case of 

 the species here under discussion can be cited as a very instructive 

 example. Orthoceras lamarcki is cited by Hyatt as a type 

 of his genus Protocycloceras which comprises " annulated ortho- 

 ceracones and cyrtoceracones without longitudinal ridges " while 

 another presumably phylogenetically successive genus Cycloceras is 

 proposed for " annulated orthoceracones and cyrtoceracones with dis- 

 continuous longitudinal ridges." Forms with annulations and con- 

 tinuous longitudinal ridges, either in early or ephebic stages are put 

 even under a different family, the Kionoceratidae. We find now 

 however that this type of the genus Protocycloceras not only does 

 not fail to be without any longitudinal ridges — as the definition of 

 Protocycloceras requires — but has them even continuous and would 

 hence also have to be excluded from Cycloceras and from the 

 whole family Cycloceratidae. We believe therefore that the generic 

 distinctions of the Cycloceratidae and Kionoceratidae here involved 

 are based too largely on theoretic considerations to be maintainable. 



If Protocycloceras lamarcki is not so primitive in its 

 surface sculpture as Hyatt supposed, it still shows its primitive nature 

 corresponding to its very early appearance in the structure of its 

 siphimcle ; for the septal necks are not as in all later annulated forms, 

 or orthoceratites generally, short and incomplete, but complete and 

 extending from one septum to the plane of the preceding one, 

 a feature only found in the earliest growth stages of the later 

 forms, and in the ephebic stage of such primitive forms as 

 Nanno. These funnels grow first toward the interior of the si- 



