282 
NATJTILOrDEA. 
Sp. Char. The curvature in this species is always distinct, without 
being strong. Upon a chord of 60 millim., subtending the concave 
side of a young specimen, the highest perpendicular is 7 mhlim. 
The transverse section is oval, the ratio of the two diameters being 
as 4 : 3. The rate of increase is in the ratio of 3 to 4, measured in 
a length of 35 millim., in the septate part of the shell. The body- 
chamber occupies between ^ and | of the total length of the shell ; 
the aperture is in the plane of the last septum, it is slightly emar- 
ginate upon the ventral border. The distance between the septa is 
equal to about of the corresponding ventro-dorsal diameter. The 
siphuncle is situated close to the convex border ; its elements are 
elongated and cylindrical. The surface of the test is ornamented 
with transverse, irregularly spaced, upwardly imbricating folds, and 
these are covered with fine lines running in the same direction. 
RemarTcs. The species most closely allied to this one is J/. sociale, 
Barr. (pi. cviii. &c.) ; but the latter is much more strongly arcuate 
and increases less rapidly, its ornaments are also more strongly de- 
veloped. 
Horizon. Etage E, bande e 2 ( = Salopian). 
Localities. Lochkow, TViskocilka, Bohemia. 
Fairly well represented in the Collection. 
Cyrtoceras (Meloceras) sociale^ Barrande, sp. 
1848. Cyrtoceras sociale, Barrande, Haidinger, Berichte fiber die Mit- 
theil. von Freund, der Natiu’wiss. in Wien, Band iv. p. 209. 
1852. CyHoceras sociale, Gumbel, Fauna der Vorwelt, Band iii. Abth. i. 
p. 209. 
1867. Cyrtoceras sociale, Barrande, Syst. Sil. de la Boheme, vol. ii. 
pt. i. p. 530, pi. cviii. ft. 1-12, pi. ccv. fi. 1-7. 
Sj). Char. Shell strongly curved, more especially in the apical 
portion. Upon a chord of 67 millim., subtending the concave side 
of the specimen, the highest perpendicular is 29 millim. The trans- 
verse section is oval, the ratio of the two diameters being as 6:5. 
The body-chamber is short, occupying scarcely -1 of the total length 
of the shell in the larger examples ; the aperture is parallel to the 
plane of the last septum. The distance between the septa equals 
about \ of the corresponding diameter of the shell. The siphuncle is 
very near the convex border ; its elements are elongate and cylin- 
drical. The test is ornamented with somewhat irregular transverse 
folds or narrow bands, which become coarser as the shell attains 
adult dimensions, the whole being covered with exceedingly fine 
transverse lines, visible only with the aid of a lens. 
