CKPHALOPOI \ 777 



pr. 



With all the knowledge that we can derive from th? works of others ami our 

 own observation* a- to the carls >holl-^n>\vth in this genus, there seems to be no 

 ..... 1 IVMOD far MIBining that tlir-oli.l -ln-atli m (.'.'"""" //- -\\a- pn>tni.|r. I Ki-ycui'l 



the septate portion of the shell, as is the case in our new genus AVi;in. The close 

 relation between \tinn<>. < '<nn> /</<; -,,s ami I'ilo.eraa is evident. Nanno has a prominent 

 -olnl guard at the apical extremity of the sipho, which is perhaps proportionally 

 longer than the solid sheath of Camerocrrus, and the sipho in Nanno bears evidence of 

 I'fiiij/ discontinuous through the later air-chambers. The siphones of Nanno being 

 extremely lateral. in position show the oblique attachments of the septa common in 

 several species of Cameroceras. 



There are here several species of Cmneroceras which are indicated by the differ- 

 ences in these siphones, but which can not be otherwise described, as the character 

 of the septate and external portions of the shell are not known. Various of these 

 are illustrated, showing wide differences of form, partially resulting from differences 

 in position in the conch, others showing a considerable variation in the depth of the 

 aii chambers, and still others having the form of Colpoceras, a genus founded upon 

 a -ipho of Cameroeeras. 



Such species, whose characters have been made out with some degree of 

 certainty, are described below. 



I'AMKKOCKKAS I-ROTKIKOKMK //<///. M7. 



TI.Ml \l. VIM. Hi.- I ri.ATK XI.IX. KKi. 2: I'l.ATK U > It.- I'l.VTI I.I. HI.-. I-I; 



IM.ATF. 1.1 1 1. FIUK0-&. 



A,'/i'/ocen proteiforme, II MI :-7. rahi-nntolmty <.f New York, vol. I. p. JOB, Pis. XLVI, MKK. In //. 

 \ in. Me- I. ^ ( -I. .1. 4: xi.xi\ tln<. la, ; L, fl{8. 13: LII. figs, la l>; LIII, fin*, lo-e 

 ' (E. maanirrntrumj, Z: LV, flg. 1 ( /:. <lui>licatumf ) ; l.vn, tl;s. la, 6. 



To this species, so abundantly illustrated in the work cited, may be referred the 

 majority of individuals of Cameroceras occurring in the Trenton limestone of Minne- 

 ^mce the elaborate account of these fossils given by professor Hall, no 

 attempt has been made to supplement or revise the original determinations, but it 

 iiui-t now be observed that the number of species into which the genus was there 

 divided and, especially, the numerous varieties ascribed to Endocera* proteiforme can 

 hardly be regarded a- wholly valid. At that early date, nearly a half-century ago, 

 the structure of these remarkable bodies was, naturally, less clearly understood than 

 to-day. Professor Ilall'< oloervations were almost the pioneer explanations of the 

 peculiar siphonal structures and are by all means the fullest and most comprehensive 

 illustration of these structures that has been given even to this day. A very natural 

 misconception of certain structural features introduced some errors which, in the 



