TKOCHOCEKATIDJE. 
15 
Lituites, Sailer, 1855^; Lituites, Eichwald, 1860^; Gyroceras, Wiii- 
chell & Marcy, 1865^; Sphyradoceras, Hyatt (pars), 1883^; TrocJiolites, 
Hyatt^ (pars), 1883.] 
Gen. Char. Shell more or less helicoidal, composed of few whorls, 
the number rarely exceeding two, all of them exposed. The enrol- 
ment is sometimes dextral, sometimes sinistral, examples of the 
former, howeyer, being by far the most numerous. The transyerse 
section is subcircular, or elliptical, more rarely subquadrangular. 
The body-chamber is scarcely dilated, but there is sometimes a slight 
constriction near the aperture. The proportions of the body-chamber 
yary from i to -jL the length of the entire shell. The aperture is 
simple and conforms to the outline of the body-chamber ; there is a 
slight emargiuation in the median line of the conyex border. The 
septa are rather approximate, their distance yarying between J and 
jV the yentro-dorsal diameter. The siphuncle yaries in position 
from near the centre to the external or conyex margins, but in one 
species {Troch. secuJa, Barr.®) it is internal ; its elements are slightly 
inflated between the septa. 
Trochoceras ranged from the Cambrian to the Heyonian, but the 
genus attained its highest deyelopment in the Silurian. It has been 
described under the name Lituites from Xorth America (Canada ') 
and Sweden from rocks of Cambrian and Ordoyician age respectiyely, 
while the Silurian rocks contain abundant species in Bohemia, 
England, and the United States. Seyeral species are recorded from 
the Deyonian of the last-named country and one species from 
rocks of Lower Devonian age in France®. The specimen from Ger- 
many (Nassau) described by the Brothers Sandberger under the name 
* British P.al. Foss. fasc. iii. Appendix, p. viii {L. cornu-arieiis). 
^ Lethsea Kossica, vol. i. p. 1298. 
^ Mem. Boston Soc. Nat. Hist. vol. i. p. 102. 
‘ Proc. Boston Soc. Nat. Hist. vol. xxii. p. 298. 
“ Ibid. p. 267, Trocholites {Liiuites) undatus. 
® Syst. Sil. de la Bohdme, vol. ii. pt. i. pi. xxx. If. 1-6. 
L. Farnsworthi, Billings (Pal. Foss. vol. i. 1861-1865, p. 21), is in all pro- 
bability a Trochoceras ; it is certainly not a Lituites, as that genus is defined by 
Lessen and Noetling, whose interpretation is adopted in this Catalogue. It is 
more difficult to speak of the other species recorded by Billings, because they 
are not figured, but, judging by the descriptions of L. imperator and L. Apollo, 
these also belong to Trochoceras. To the last-named may be referred likewise 
L. undatus. Hall (see infra, p. 41). 
^ Hall, Pal. New York, 1879, vol. v. pt. ii. p. 390. 
® Trochoceras Lorierei, Barr., from Sarthe : — ‘ Defense des Colonies,’ iii. p. 278. 
