438 NEW YORK STATE MUSEUM 



Observations. Our specimen represents but the apical portion of 

 this form which has been described by BilHngs from more mature 

 parts. Nevertheless there can be but little doubt of its identity 

 with Billings's species in view of the like rate of growth, character- 

 istic great depth of the cameras, strong convexity of the septa and 

 small siphuncle. The dimensions of our specimen are : length 34 

 mm ; smallest width 4 mm ; greatest width 7 mm ; rate of growth 

 I mm in 10 mm ; 3 cameras in space of 10 mm ; depth of septum 

 one third that of camera; width of siphuncle one sixth that of 

 conch. In the Chazy specimen the siphuncle is entirely tubular 

 while Billings describes it as very slightly nummuloidal, but since 

 it frequently begins tubular and becomes more or less nummuloidal 

 in later growth stages, this difference can not be considered as of 

 great importance. 



Family cycloce^jrjvtiida.e 

 Genus protocycloceras Hyatt 



The genus Protocycloceras has been proposed by Hyatt to receive 

 the most primitive cycloceratids. It is defined as consisting of annu- 

 lated orthoceracones and cyrtoceracones without longitudinal ridges 

 and with large siphuncles. As genotype the form described in the 

 following pages is named which, from its occurrence in the middle 

 Beekmantown beds of New York, can be considered as the earliest 

 or one of the earliest annulate forms known. 



The establishment of this genus and the arrangement of the 

 succeeding genera of the Cycloceratidae presuppose the antecedence 

 of the annuli or of the transversal portion of the surface sculpture 

 (annuli and frills) to the longitudinal portion (ridges and lines). 

 While, in apparent harmony with this view, sculpture casts from the 

 Beekmantown dolomite fail to show any traces of longitudinal sculp- 

 ture lines, there has been found associated with them a fragment 

 of a shell in the neanic stage [pi. 15, fig. 6], which has no other 

 ornamentation but strong longitudinal ridges. In view of the p.sso- 

 ciation of this conch with the annulated ones and the failure to ob- 

 serve other species of orthoceracones or of slightly curved cyrtocera- 

 cones in this bed, the reference of this little shell to the nepionic 

 stage of the annulated form offers itself as the most plausible con- 

 clusion. The latter is supported by our finding among the material 

 collected by Professor Rominger from the Fort Cassin beds at Fort 

 Cassin a fragment of a young conch of this species exhibiting both 

 annulations and sharp continuous longitudinal lines in excellent 

 preservation [pi. 16, fig. i]. 



