44 
NAUTILOIDEA. 
section. Siphuncle subcentral, or near the concave border. Body- 
chamber exceeding half a volution in length. Septa numerous, the 
sutures forming a shallow sinus upon the ventral surface of the shell ; 
necks long, extending from septum to septum, and thus constituting 
the “ holochoanoidal ” siphuncle of Hyatt b The ornaments of the 
test consist of more or less prominent annulations, which are apt to 
become obsolete upon the body-chamber. 
Remarks. Conrad’s description of Trocholites is as follows ^ : — 
“ Involute ; symmetrical ; whorls contiguous ; the back of inner 
, volutions rounded, fitting into a corresponding groove ; septa convex ; 
siphuncle near the inner margin. 
“ This genus differs from Lituites in having a submarginal 
siphuncle, and in not being extended into a straight or bent pro- 
longation. The aperture is widely different, being of a lunate 
outline, whilst in Lituites it is nearly round.” 
Following this definition of the genus comes Conrad’s description 
of his species Trocholites planorbiformis, which A. Remele^ has 
made the type of his subgenus Palceoclymenia, which he thus 
defines : — “ Whorls overlapping each other at the sides, and conse- 
quently forming an umbilicus ; higher than wide. Shell provided 
with strong spiral strise, with lines of growth crossing them.” 
How the principal character upon which this subgenus is founded, 
and by which it is separated from Palceonautilus, Remele (tj’pe 
Trocholites planorhiformis, Hall — non Conrad), is the alleged superi- 
ority of the height of the volutions to their width, as affirmed by 
Conrad in his description of T. planorbiformis. But we have seen 
that Conrad described Trocholites as having a “ lunate aperture,” 
which could not be the case if the whorls were “higher than wide”; 
e., if the dorso- ventral diameter of the section of the whorl 
exceeded the transverse. In whatever way this contradiction in 
the terms of Conrad’s description of his genus may have arisen it 
misled Bemele into supposing that the Trocholites planorbiformis of 
Conrad and Hall’s T. planorbiformis were distinct, and belonged 
even to difil'erent subgenera of Trocholites, an assumption for which 
there is no ground whatever. Hall expressly mentions in his descrip- 
1 Proc. Boston Soc. Nat. Hist. 1883, vol. xxii. p. 260. See also Part I. of 
the present Catalogue, Introd. p. v. 
^ Journ. Acad. Nat. Sci. Philadelphia, 1842, vol. viii. pt. ii. p. 274. 
® Zeitschr. der Deutsch. geol. Gesell. 1881, Band xxxiii. Heft i. p. 1. 
^ One can hardly avoid the suspicion that Conrad described Trocholites as a 
Gasteropod, for he places it among genera belonging to that class, such as 
Loxoncma, Tlatyostoma^ &c. 
