222 
AUG. F. FOERSTE 
nomic sinus. However, since Orthoceroids do not have an hypo- 
nomic sinus, this method of orienting the conch can not be used 
for them. When the transverse striae slope distinctly downward 
from one side of the conch to the other, the lower part of their 
course is supposed to correspond to the hyponomic sinus, at least 
in those forms which are not curved lengthwise. It may be 
acknowledged freely that in the present state of our knowledge 
of the Orthoceroids the terms dorsal and ventral are used loosely. 
In the absence of all other criteria, that side of the conch which 
is nearest the siphuncle is called the ventral one, lat least pro- 
visionally. 
Banding is by no means confined to the genus Geisonoceras, It 
occurs also in breviconic forms, as indicated by Hyatt,^° and in 
some species of Actinoceroids. 
21. CYCLOCERAS McCOY 
The genus Cycloceras was defined by McCoy^® as consisting of 
“those conical species marked with prominent concentric rings, 
and having the surface frequently sculptured with transverse 
scaly laminae, and often decussated; siphuncle dorsal.’^ This 
description is accompanied by a small figure with vertical striae 
or ribs, but the figure does not resemble any species described 
or listed by him in the text. Among the species known at that 
time, it most resembles Orthoceras rugosum Fleming, as repre- 
sented by Phillips,^^ and that species is therefore regarded here 
as the genotype. In this figure the annulations are tuberculated 
by longitudinal echinated lines, of which there are apparently 
about 18 on the entire circumference of the conch. The expres- 
sion, “siphuncle dorsal,’’ at present would be changed to siphuncle 
ventral. 
None of the species described or listed by McCoy in the body 
of his text agrees with his description of the genus in the posses- 
sion of vertical lines of any kind. The first species mentioned 
was originally described by Fleming-® as Orthocera annularis, 
Fleming’s illustration is reproduced herewith as figure 4, plate 
XXV. The surface of this species is said to be smooth, except 
Hyatt, A., op. cit., p. 275. 
Syn. Garb. Foss. Ireland, 1844, p. 6, fig. 6. 
Geology of Yorkshire, 1836, pL 21, fig. 16. See also Fleming, Ann. Phil, 
vol. 5, 1815, p. 203, pi. XXXI, fig. 9. 
^ Ann. Phil., vol. 5, 1815, p. 203, pi. 31, fig. 8. 
