CYETOCERATID^. 
301 
Cyrtoceras (Meloceras) arbanum, Barrande, sp. 
1867. Cyrtoceras nrhanum, Barrande, Syst. Sil. de la Bolieme, vol. ii. 
pt. i. p. 699, pi. cxcviii. £f. 11-20. 
Sp. Char. Shell elongated, having a considerable and uniform 
curvature ; upon a chord of 80 millim., subtending the concave border, 
the highest perpendicular is 13 millim. The transverse section is 
circular. The increase in the septate part is in the ratio of 1 : 3, in 
a length of 54 millim. The body-chamber occupies about ^ of the 
total length of the shell. The distance between the septa is equal 
to about i the diameter of the shell. The siphuncle is situated 
nearly midway between the centre and the convex border ; its ele- 
ments are cylindrical. The shell-ornaments consist of subacute 
annulations barely 1 line distant from each other where the shell has 
a diameter of 5 lines. These coarser ornaments are covered with 
extremely fine transverse striae, which give a silky appearance to the 
surface of the test when seen under a low magnifying-power. 
Remarks. This species resembles M. semitectum, Barr., sp. (pi. 
cxcviii.), and M. nitidum, Barr., sp. (ibid.), in its general form, but 
these last are distinguished by having a considerable part of the 
shell, below the aperture, devoid of annulations. 
Horizon. Etage E ( = Salopian). 
Localities. Dlauha Hora, Konieprus, Bohemia. 
Fairly well represented in the Collection. 
Brevicoxes. 
Cyrtoceras (Meloceras) mundum, Barrande, sp. 
1867. Orthoceras mundum, Barrande, Syst. Sil. de la Boheme, vol. ii. 
Texte iii. (1874J, p. 64, pi. clxxxvi. ff. 1-34, pi. cccclxxxviii. 
case iv. If. 1-3. 
Sp. Char. Shell straight in most specimens, sometimes very slightly 
curved. The apex, instead of being acute, is bluntly rounded. The 
increase in diameter is very rapid ; it varies from 1 in 2 to 1 in 3, 
some specimens tapering more slowly than others. The transverse 
section is circular in some examples, elliptical in others. The body- 
chamber is well developed, its length equals at least ^ that of the 
entire shell. The distance between the septa is equal to about ^ 
the diameter of the shell. The siphuncle is remarkable for the 
variability of its position in different specimens. In some it is 
central throughout the whole of the septate part ; in others it shifts 
its position nearer to the border until this latter point is actually 
reached; its elements are cylindrical. The ornaments of the test 
