CTKTOCEEATTDJS. 
313 
1849. Lituites falcatus, Quenstedt, Petrefactenkunde Deutschlands, 
Band i. Abth. i. p. 50, tab. i. ft'. 15, a, b (copied from Scblotheim). 
1860. Cyrtoceras falcatiim, Eicbwald, Letbaea Rossica, toI. i. Seconde 
Section de I’Ancienne Periode, p. 1280, pi. 1. ft. 8, a, b. 
1867. Cyrtoceras falcatum, Barrande, Syst. Sil. de la Bobeme, vol. ii. 
pt. i. p. 376. 
[Not 1833. Orthoceratites falcatus, Steininger, M6m. Soc. Geol. de 
France, vol. i. pt. i. p. 369.] 
Sp. Char. Shell elongated, curved, laterally compressed. The 
curvature well marked, so that upon a chord of 24 lines subtending 
the concave side of an incomplete specimen 3 inches in length the 
highest perpendicular is 4 lines. The transverse section is elliptical. 
The body-chamber has not been seen in a complete state. The 
septa are numerous and strongly waved. The siphuncle is situated 
submarginally, close to the convex border of the shell. The test, 
which is admirably preseiwed in one of the specimens in the Collec- 
tion, is ornamented with subregular lines of growth, which have an 
upward imbrication. 
RemarTcs. M. Eichwald figures a portion of the body-chamber of 
this species {loc. cit. f. 8, «), and in the middle of it there is a double, 
transverse, curved groove, and a little above this is another super- 
ficial rounded depression, which Eichwald supposes to be a muscular 
impression. 
Horizon. O/’tAoc^rrts-Limestone ( = Arenig). 
Locality. Beval (Esthonia), Russia. 
Fairly well represented in the Collection. One of the specimens 
was transferred from the Museum of Practical Geology. 
SILURIAN SPECIES. 
Cyrtoceras (Ooceras) approximatum, 
J. de C. Sowerby, sp. 
1839. Orthoceras approxhnatum, J. de C. Sowerby, in Murchison’s Sil. 
Syst. p. 642, pi. xxi. f. 22. 
1854. Cyrtoceras approximatum, Salter, in Murchison’s ‘ Siluria,’ pi. xi. 
f.4. 
1854. Cyrtocet'as approximatum, Morris, Cat. of Brit. Foss. 2nd ed. 
p. 302. 
1882. Cyrtoceras approximatum, Blake, British Foss. Cepb. pt. i. p. 172, 
pi. XX. fi*. 1, 1 a. 
Sp. Char. ‘‘ The section is circular. The rate of increase is very 
slight at the smaller end, and almost zero at the larger. The curva- 
ture is slight, having a radius of 7| inches. The surface is only 
