CYRTOCERATII)^. 
291 
section is oval, tlie ratio of the two diameters being as 4 : 3. The 
rate of increase is very rapid, being about 1 in 2, measured in the 
septate part of the shell. The body-chamber is proportionately very 
large, occupying at least half of the total extent of the shell, and 
its bulk is equal to twice or three times that of the septal chambers. 
The outline of the aperture corresponds with that of the transverse 
section, but it expands rapidly in the direction of the ventro-dorsal 
diameter. The distance between the septa is equivalent to about 
jL of the ventro-dorsal diameter. The siphuncle is situated close 
to the concave border, and is composed of nummuloidal segments 
whose breadth increases very rapidly : thus, between the last 
two septa it occupies 4 of the ventro-dorsal diameter, whilst at the 
fifteenth septum below it is only ^ of the same. The form of the 
segments is oval, and they are much elongated ventro-dorsally, their 
interior is filled with an “ organic deposit ” of a peculiar appearance. 
The test is ornamented with fine and pretty regular transverse striae, 
which are convex towards the aperture on the sides of the shell, 
whilst they are concave on the convex border, and on the concave 
border they make a relatively deep and narrow sinus. 
Remarlcs. This species is distinguished from its congeners, such 
as M. neutriun, Barr., sp. (pi. clxv.), and 21. Murchisoni, Barr., sp. 
(pi. clxv.), by the great rapidity of its expansion, by its curvature, 
by the form of its siphuncle, organic deposit, &c. 
Horizon. Etage E, bande e 2 ( = Salopian). 
Localities. Lochkow, Konieprus, Bohemia. 
Well represented in the Collection. 
Cyrtoceras (Meloceras) debile, Barrande, sp. 
1848. Cyrtoceras clehile, Barrande, Ilaidinger, Berichte liber die Mit- 
theil. von Freund, der Naturwiss. in Wien, p. 208. 
1852. Cyrtoceras dehile, Giebel, Fauna der Vorwelt, Band iii. Abth. i. 
p. 209. 
1867. Cyrtoceras dehile, Barrande, Syst. Sil. de la Boheme, vol. ii. pt. i. 
p. 655, pi. clxviii. ff. 25-29, pi. clxxvii. ff. 19-24. 
Sp. Char. Shell variable in its amount of curvature. Upon a 
chord of 45 to 50 millim. the highest perpendicular varies from 2 
to 5 millim. The transverse section is nearly circular. The rate 
of increase is 1 in 4, measured in the septate part of the shell. The 
body-chamber is well developed, its length being a little less than 
half that of the entire shell, and its bulk nearly three times that of 
the septate part. The aperture exhibits a distinct though shallow 
sinus on the concave border. The distance between the septa 
amounts to about g the diameter of the shell. The siphuncle is 
u2 
