REPORT OF THE STATE PALEONTOLOGIST I903 



337 



On the same principle P . n e w t o n - w i n c h e 1 1 i should be 

 removed from the holochoanitic Piloceratidae and brought under the 

 Orthochoanites, where, as far as I am aware, it constitutes a new 

 genus (Clarkoceras). 



A further character quite significant of the advance of 

 Clarkoceras newton-winchelli beyond the typical 

 Piloceras stage is to be seen in the re- 

 duction of the endosiphosheaths of which 

 only two were observed in a specimen of 

 Avhich only a small apical portion is miss- 

 ing [see fig.26]. These leave large endo- 

 •siphuncular chambers betw^een them which 

 are not filled by depositions of lime car- 

 honate, as the much smaller chambers 

 in the species of Piloceras are. The 

 ccndosiphotube is only indicated by the 

 perforation of these endosiphosheaths 

 and has lost its own wall The entire 

 •endosiphuncular structure is distinctly in a 

 process of dissolution, resulting from the 

 reduction of the size of the siphuncle in 

 -consequence of the more complete with- 

 drawal of the visceral cone. In Balto- 

 ceras the process of dissolution has gone already a step farther and 

 all traces of endosiphosl^eaths have been lost notwithstanding the 

 ■still considerable width of the siphuncle. 



Summary 



1 The conch of C a m e r o c e r a s b r a i n e r d i from the 

 Upper Beekmantown formation begins with a long slender pre- 

 septal cone or nepionic bulb, which terminates anteriorly with a 

 slight constridion where septation sets in. 



2 The nepionic bulb and the middle (neanic) portion of the 

 siphuncle are filled by endosiphosheaths, while the anterior 

 (ephebic) portion is empty. 



3 The empty anterior portion is closed in apicad direction by 

 the final endosiphoshcaih, which incloses tlie endosiphocone 



Fig. 26 Clarkoceras new- 

 ton-winchelli Clarke (sp.). 

 Median vertical section of a 

 specimen, xr.5. (Copy from 

 Clarke) 



t 



