NAUTILIDA. 53 
chamber—the cavity affecting at least seven of the uppermost 
septa, if not the whole. 
rHIsoA, Montf. Shell ovate-elongate, cucumber-shaped ; appar- 
ently two siphons running parallel the whole length of the shell, 
one of which traverses a sort of narrow lateral cavity ; there are 
also a number of false siphons or holes, which do not extend the 
entire length of the shell. 7. siphonalis, Serres (xxix, 82, 83). 
Jurassic; France. 
GontocEerAs, Hall, 1847. Shell flattened, with extremely salient 
angles ; septa sinuous; section of shell, an extended ellipse with 
projecting angles; siphuncle ventral. G. anceps, Hall (xxx, 94, 
95). L. Silurian; N. America. 
COLPOcERAS, Hall. This is probably only a siphon of one of 
the larger species of Orthocerata. C. virgatum, Hall (xxx, 96). 
L. Silurian; New York. 
DICTYOCERAS, Hichw.,1859. Is probably an Orthoceras covered 
by a bryozoan or coral. 
TREMATOCERAS, Whitfield. Tube, septa and siphuncle like 
Orthoceras, but with a line of elongated, raised tubercles along 
one side of the shell, which have formed perforations at certain 
stages of growth, probably confined to the outer chamber as 
openings, which were closed as the animal extended the shell, 
and before the septa opposite them were formed. Type 7’. Ohio- 
ense, Whitfield. Upper Helderberg group, Ohio. 
f Potortuus, Gabb, 1861. 
The aggregated mass of specimens forming the type of this 
genus was originally referred to Teredo; subsequently, in de- 
scribing the genus, Mr. Gabb referred it to Vermetidx, and in 
1872 he finally believed it to be a cephalopod connecting the 
Orthoceratide with Beatrice. The aggregate character, the 
long, narrow, irregular tube, the non-molluscan character of the 
partitions forbid this determination. I am convinced that 
Polorthus is not a mollusk, and Beatricea itself is now referred, 
doubtfully, to the sponges. | 
Crinoceras, Mascke, 1876. 
Distr—C. dens, Mascke (xxviii, 73). Erratic L. Silurian 
blocks ; Prussia. 
Shell conical (allied to Loxoceras, M’Coy), the siphuncle side 
straight, the others more or less curved; a constriction below 
the body-chamber. Septal border with an obtuse-angled saddle 
on the siphuncle side, with gently rounded lobes and two slightly 
marked lateral saddles. 
, Bactrites, Sandberger, 1842. 
Syn.—Stenoceras, d’Orb, 1850. 
Distr.—13 sp. Silurian to Trias.; Germany, etc. JB. gracilis, 
Sandb. (xxxii, 22). Nassau. 
