290 
NAUTILOIDEA. 
1852. Cyi'toceras aduncum, Giebel, Fauna der Vorwelt, Band iii. Abth. i. 
p. 209. 
1867. Cyrtocerafi aduncum^ Barrande, Syst. Sil. de la Bobeme, vol. ii. 
pt. i. p. 683, pi. clxix. IF. 9-14, pi. clxxxi. fF. 10, 11. 
Bp. Char. Shell large and of robust habit, having only a slight 
curvature in the apical portion, the rest being nearly straight. The 
transverse section is nearly circular. The rate of increase is about 
1 in 2, measured in the septate part of the shell. The body-cham- 
ber, which occupies nearly one half of the total length of the shell, 
dilates less rajudly than the septate part. The aperture is parallel 
to the plane of the last septum ; it has a strongly marked sinus on 
the concave border. The distance between the septa is equal to 
about ^ the diameter of the shell, and their convexity equals about 
-1- of the same. The siphuncle is situated in close proximity to the 
concave border, without, however, touching it ; it is composed of 
flattened nummuloid segments disposed obliquely, in conformity 
with the inclination of the septa ; the width of the segments is 
equal to ^ the diameter of the shell. The test is ornamented with 
transverse lamellose striae having a direct imbrication ; they are 
but rarely preserved. 
MemarJcs. M. specioswn^ Barr., sp. (pi. clxx.), resembles M. adun- 
cum in its general appearance, but it expands more rapidly, and the 
siphuncle has quite a different form (pi. clxxviii. f. 3). 
The appearance of the siphuncle in the present species recalls that 
of Actinoceras. 
Horizon. Etage F ( = Downtonian). 
Locality. Konieprus, Bohemia. 
llepresented in the Collection by two examples. 
Cyrtoceras (Meloceras) Beaiimonti, Barrande, sp. 
1848. Cyrtoceras Beaumonti, Barrande, Ilaidinger, Berichte iiber die 
Mittheil. von Freund, der Naturwiss. in Wien, p. 209. 
1852. Cyrtoceras Beaiimonti, Giebel, Fauna der Vorwelt, Band iii. 
Abth. i. p. 209. 
1867. Cyrtoceras Beaumonti, Barrande, Syst. Sil. de la Boheme, vol. ii. 
pt. i. p. 685, pi. clxv. fl*. 21-26. 
Bp. Char. The curvature in this species represents the maximum 
attained in the genus Cyrtoceras ; but the initial point of the shell 
is at some distance from the body-chamber, the latter projecting 
considerably beyond it as in some other genera, such as the endo- 
gastric forms of Oomphoceras, &c. The initial point of the shell 
instead of being acute, as in other allied forms, is rounded ; it is 
covered by the calotte coniqne (pi. clxv. f. 21). The transverse 
