IIAI.OI.I.\ 775 



mmcerm*. | 



mi* ' \MI K", KKAS, Conrad. 18 



/ .<.... r.u HM : Ml 



The collection i> fairly .il>uii<l;iiit in specimens referable to this genus. Few, 

 however, arc Mittiriently complete to justify the determination of their specific 

 < liar.i<-t-r>. though the evidence afforded by them indicates the probable presence of 

 several species. Of more interest than the variation in specific features is the 

 interesting illustration of the structure of the sipho which is represented by many 

 and various forms of internal casts of the organ. With all that has been written 

 upon tlic relation of the sipho of this genus to the septa and conch, there still remains 

 much to l>e learned in regard to the structure of Catneroceras, and some light is 

 thrown upon obscure points by these specimens. We have here adopted without 

 reserve Conrad's term Cameroctras in place of the more generally accepted name 

 l.mloceras. Whitfield has employed the former term with a suggestion that there 

 may prove to be a generic difference in the two structures, but this seems to us, 

 with the present evidence, scarcely possible. The distinction which has been 

 recognized between the two by Hyatt is that in Endoceras the siphon is not lined by 

 a continuous shell layer but is composed of a succession of septal funnels, overlapping 



heir edges, while in Cumeroceras (which this author regards as a synonym of 

 Sannionites, Fischer de Waldheim, 1837), the siphon is a continuous layer. The 

 typical species of Endocerus ( /.'. />rokiforme Hall) is vastly better known than that 

 of Cameroceras (C. trentoneme), and while it has been impossible for me to carry out 

 a generic distinction in the two, the fact must be recognized that the latter term 

 was introduced in 1839 and the former not until 1847. Conrad, also, in 1839 employed 

 the name Diploceras (D. vanuxemi, type) for a shell from Trenton Falls, N. V .. which 

 is unquestionably a Camerocems, and the species probably the same as Endo- 

 /</ it'nrmt. Hall*, Whitfieldf, DewitzJ, HolmjS, Foord " and others have shown 

 the existence of a continuous sheath situated at, and composing the apical portion 

 of the sipho, often thick-walled, and extremely so about the apex itself. These have 

 been sometimes termed "embryo-tubes" and also "siphonal sheaths," as though 

 they existed within the sipho and were not an integral part of the sipho itself. 

 Such bodies, of which internal casts abound in the Trenton formation of Minnesota, 

 are the thickened extremital portions of siphones; the septa lie against them (or at 

 least, against their upper portions) in a normal position, and above its free 

 edges the sipho is a discontinuous sheath composed of the overlapping and 



Bull. Amr. MM. Nat. lll.i > ..I I. DO. I. pp. 1 



PmlcoMolonr of New York. vol. L, pp. W <f . .. pi.. M-M, B. eu-. UI7. 



-ohr der deuterb. t col. OexlUoh.. vol. null. pp. I7I-M. pi. * 17. MO. 

 I Dam*, and h> wr . l-ilh.ololocbciM Abbndlunrn. Hod 111. Heft I. IMA. 

 I Aon. od M*. Sat II tot.. DM- W7. pp.1 



