42 
NAUTILOIDEA. 
Orthoceras styloideum, Barrande. 
1866. Orthoceras styloideum, Barrande, Syst. Sil. de la Boheme, 
vol. ii. Texteiii. 1874 (janvier), p. 553, pi. ccxxxix. £f. 5-8, pi. 
ccclxv. ff. 1-8, 10, 11. 
1873, Orthoceras styloideum, Barrande, Distrib. des C4pli. dans les 
Contrees Siluriennes, p. 50 (Extrait du Syst. Sil. de la Boheme, 
vol. ii. 4me ser.), 
1876. Orthoceras styloideum, Tromelin & Lebesconte, Assoc, Fran?, 
pour I’avancement des Sciences, 4me Sess. (Nantes), p. 601. 
Sp, Char. Shell very slender. Section generally a little ellipti- 
cal. Rate of increase 1 in 24. Septa distant about ^ the diameter. 
Body-chamber a little variable in its relative length, the extreme 
limits being 4^ times and 7 times the basal diameter. The aper- 
ture has an obliquity of about 10° from the horizontal. The 
siphuncle is eccentric, and is placed about 4 across the longer 
diameter. Surface markings consisting of faintly impressed, very 
fine striae. The test is rarely preserved, as it is nearly always 
torn away in separating the specimens from the matrix. 
BemarTcs. M. de Yerneuil cites this species from St. Beat (Hautes- 
Pyrenees), whence it was brought to him by M. Leymerie, with 
other characteristic Upper Silurian fossils. 
M. Barrande believes that this species, like 0. truncatum, &c., 
shed or truncated its shell, and he supports his 02 )inion upon the 
following considerations. He says : “ The constant absence of the 
initial part of the shell, in more than a thousand individuals of this 
species that we have collected, leads us to conclude that they have 
undergone regular and normal truncation. This supposition of 
natural truncation in Orth, styloideum seems confirmed by this fact, 
that the septa of our specimens are constantly destroyed, save in 
very exceptional cases. These exceptions relate almost solely to 
the terminal septum of the great [body] chamber, that is to say, to 
that one which remains in contact with the souree of life and of 
preservation, up to the death of the moUusk.” M. Barrande further 
observes that he has not recognized in any case in this species the 
reparation of the truncated extremity. 
Horizon. Etage E, bande e 1 ( = Salopian); Calcaires ampeliteux 
( = Third Fauna of Barrande). 
Localities. Butowitz, Bohemia; FeugueroUes (Calvados), France. 
Orthoceras aperiens, Barrande. 
1868. Orthoceras aperiens, Barrande, Syst. Sil. de la Boheme, vol. ii. 
Texte iii. 1874 (janvier), p. 475, pi. cccxliv. ff. 12-23. 
Sp. Char. Section somewhat variable in outline. Sometimes 
