34 
NATJTILOIDEA. 
Orthoceras severum ?, Barrande. 
1866. Orthoceras severum, Barrande, Syst, Sil. de la Boheme, vol. ii. 
Texte iii. 1874 (janvier), p. 384, pi. ccxix. ff. 1-4, 7-8; ? pi. 
ccxxi, ff. 4, 5 ; pi. ccxxv. ff. 14-17 ; ? pi. ccxxix., pi. cclxxx. 
AT. 15-17 ; pi. ccci. ff. 1-5 ; pi. cccii. ff. 1-7 ; pi. cccx. ff. 12-15 ; 
pi. ccccxliii. ff. 7, 8. 
1876. Orthoceras severum?, Tromelin and Lebesconte, Assoc. Fran9. 
pour I’avancement des Sciences, 4me Sess. (Nantes), p. 621, and 
Tabl. D. No. 32. 
Sp. Char. Section circular. Bate of increase about 1 in 10. 
Septa distant about f the diameter. Body-chamber known only by 
incomplete and isolated fragments, whose specific identity is not 
established beyond a doubt. Siphuncle a little eccentric. Surface 
with subregular imbricating (?) striae, which are visible, as a rule, 
without the aid of a lens. The so-called organic deposit of Barrande 
is well developed in the chambers. 
Horizon. Calcaires ampeliteux ( = Third Fauna of Barrande). 
Locality. Feuguerolles (Calvados), France. 
Two imperfect specimens. 
Orthoceras bifrons, Barrande, var. geminomm, Barr. 
1870. Orthocd'as bifrons, Barrande, var. geminorum, Barr. Syst. Sil. 
de la Boheme, vol. ii. Texte iii. 1874 (janvier), p. 398, pi. 
ccclxvii. ff. 12, 13, 15. 
^p. Char. Shell very slender. Section somewhat elhptical. 
Bate of increase very gradual, scarcely perceptible in some 
examples, about 1 in 13 in others. Septa very variable in their 
distance apart, even in the same individual, generally about \ the 
diameter, which is also the amount of their convexity. The body- 
chamber is not well developed. Its length is about 4 times the 
diameter of the base, or about -J- the total length of the shell. 
Siphuncle very slightly eccentric. 
The surface ornamentation, instead of being composed of conti- 
nuous striae, as in 0. bifrons, has alternately long and short striae. 
The long ones are paired, and they nearly encircle the shell, dis- 
appearing or becoming very feeble upon the dorsal surface. 
Between these principal striae there occur two or three secondary 
ones, which are strongly marked upon the ventral side, but become 
obsolete towards the middle of the lateral surface. Faint longi- 
tudinal lines may also be seen, especially in that part of the shell 
which is not reached by the transverse striae. M. Barrande 
appears to have overlooked these. The striae above described have 
a downward imbrication. There are about six of them per line. 
