296 
NAT7TIL0IDEA. 
voL ii. pt. i. p. 669, pi. cxlvi. ff. 12-15, pi. ck. ff. 1-9, pi. clxiii., 
pi. ccxxiii. ff. 18, 19. 
1877. Cyrtoceras quad-rectum^ Barrande, ibid. Suppl. et S^r. tardive, 
p. 176, pi. diii. ff. 12-16. 
Char. Shell curved only in the apical portion ; upon a chord 
of 75 millim., subtending the concave side, the highest perpendicular 
is 2 millim. The transverse section is eUiptical in the greater 
number of specimens examined, the ratio of the two diameters being 
as 8 : 7 ; in others it was found to be circular. The rate of increase 
is also subject to variation ; thus, in one specimen measured it is 
in the ratio of 1 : 2 in a length of 66 millim., measured in the 
septate part ; in another it is in the ratio of 2:5 in a length of 
45 millim., measured in the apical portion of the shell. The body- 
chamber is well developed, occupying somewhat less than of the 
total length of the shell. The aperture has a weU-marked sinus 
upon the concave border. The distance between the septa is very 
regular, and amounts in adults to about -jL- of the diameter of the 
shell. The siphuncle is situated close to the concave border and is 
cylindrical. The test is ornamented with transverse, regular, very 
prominent plications, having a dii’ect imbrication : they become 
stronger in the upper part of the shell. 
Remarks. This species is distinguished from M. Orion., Barrande, 
sp. (pi. cxl.), which has similar ornaments; but it increases less 
rapidly in diameter, its siphuncle is nummuloidal and external, 
aud its plications rounded instead of subangular. 
M. quasi-rectum^ var. contrarium, Barr., occurs in the Wenlock of 
the Usk district, according to Blake (Brit. Foss. Ceph. pt. i. p. 175, 
pi. xix. ff. 9, 10). 
Horizon. Etage E ( = Salopian). 
Locality. Dlauha Hora, Bohemia. 
Well represented in the Collection. 
Cyrtoceras (Meloceras) parvulum, Barrande, sp. 
1848. Cyrtoceras parvuluin, Barrande, Haidinger, Berichte iiber die 
Mittheil. von Freund, der Naturwiss. in Wien, Band iv. p. 208. 
1852. Cyrtoceras parvuhim, (jii(dhe[, Fauna der Yorwelt, Band iii. 
Abth. i. p. 209. 
1867. Cyrtoceras parmdum, Barrande, Syst. Sil. de la Boheme, vol. ii. 
pt. i. p. 689, pi. clxxvii. ff. 12-18. 
1877. Cyrtoceras parvulum, Barrande, ibid. Suppl.- et Ser. tardive, p. 39, 
pi. cccclxxxi. ff. 1-15, p. 168, pi. div. 
Sp. Char. Shell strongly and uniformly curved ; upon a chord of 
