84 
NAFTILOIBEA. 
Localities. Kahlenberg, North-west Hartz ; Cramberg, near Dietz : 
Nassau. 
The specimens from the Orthoceratiten-Schiefer of Cramberg 
were transferred from the Museum of Practical Geology. 
Two imperfect specimens represent this species in the Collection. 
Orthoceras Dannenbergi, d’Archiac and de Yemeuil. 
1842. Orthoceratites Lannenhergii^ d’Archiac & de Verneuil, Trans. 
Geol. Soc. ser. 2, vol. vi. p. 345, tab. xxviii. ff. 1, 1 a. 
1847. Melia Dannenbergii, d’Orbigny, Prodr. de Paleont. vol. i. p. 53. 
1856. Orthoceras undato-lineolatum, G. & F. Sandberger, Die Verstein. 
Nassau, p. 163, Taf. xviii. ff. 6, 6«-6 d. 
1866. Orthoceras Bannenhergii^ F. A. Roemer, in Palieontographica, 
Band xiii. p. 211, tab. xxxiii. f. 16. 
1884. Orthoceras Dannenbergii, Kayser, Die Orthoceras-schiefer, in 
Jahrb. d. konigl. preussisch. geolog. Landesanst. u. Bergak. zu 
Berlin f. d. Jahr 1883, p. 18. 
Sp. Char. Shell straight. Section circular. Rate of increase 1 
in 14. Body-chamber 1^ the diameter of its base in the specimen 
figured by d’Archiac and de Yerneuil, which, however, does not 
appear to he perfect in this part. Septa distant from | to ^ 
the diameter. Siphuncle of medium thickness, central. Surface 
ornamented with transverse riblets, which are so strongly undu- 
lating as to have an obliquity in one part of their course of 
about 35° to the longitudinal axis of the shell. The riblets are 
rounded, and are about \ line distant from each other ; they are 
divided by spaces of about the same breadth. The riblets and 
interspaces are covered with fine striae, having an upward imbri- 
cation. About eight of these occupy a space equal to two riblets, 
including the space dividing the latter. 
Remarks. There is a slight discrepancy between the description 
of this species by d’Archiac and de Yerneuil, and that of the Doctors 
Sandberger, viz. in the position of the siphuncle ; the former declare 
it to be “ rather large, elliptical, and touching the edge while the 
latter, on the other hand, describe and figure it as central. I think 
there can be no doubt of the accuracy of the latter allocation of this 
organ ; and it appears to me, judging by d’Archiac and de Yerneuil’s 
figure, that those authors were misled by the crystalline infilling of 
their shell into supposing the siphuncle to be marginal. I cannot 
otherwise account for the 'disagreement between the two diagnoses. 
Assuming therefore, as did the Brothers Sandberger themselves, 
that 0. Dannenbergi and 0. undato-lineolatum are identical, the law 
