CEPHALOPODA. ea 
Cameroceras proteiforme.] 
With all the knowledge that we can derive from the works of others and our 
own observations as to the early shell-growth in this genus, there seems to be no 
good reason for assuming that the solid sheath in Cameroceras was protruded beyond 
the septate portion of the shell, as is the case in our new genus Nanno. The close 
relation between Nanno, Cameroceras and Pilocerasisevident. Nanno has a prominent 
solid guard at the apical extremity of the sipho, which is perhaps proportionally 
longer than the solid sheath of Cameroceras, and the sipho in Nanno bears evidence of 
being 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 Cameroceras 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 
air-chambers, and still others having the form of Colpoceras, a genus founded upon 
a sipho of Cameroceras. 
Such species, whose characters have been made out with some degree of 
certainty, are described below. 
CAMEROCERAS PROTEIFORME Hall, 1847. 
PLATE XLVIIL, FIGS. 1, 2; PLATE XLIX, FIG. 2; PLATE L, FIGS. 1, 2, (8 ?); PLATE LI, FIGS, 1—3; 
PLATE LIII, FIGS. 4—5, 
Endocerus proteiforme, HALL, 1847. Paleontology of New York, vol. i, p. 208, Pls. xLvt, figs. la-b, . 
2(?); XLvi1, figs. 1,2 (?), 3, 4; XLXIX. figs. la, e; L, figs. 1—3; Lm. figs. la-b; Lit, figs. la-e 
(E. magniventrum), 2: LY, fig. 1 (EH. duplicatum?); Lvu, figs. 1a, 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- 
sota. Since the elaborate account of these fossils given by professor Hall, no 
attempt has been made to supplement or revise the original determinations, but it 
must now be observed that the number of species into which the genus was there 
divided and, especially, the numerous varieties ascribed to Hndoceras proteiforme can 
hardly be regarded as 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 Hall’s observations 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 
