105 
Grnus — ORTnOCERAS, Bruguiere. 
ORTiiocErvAS SUBDIMIDIATUM, L. G. (le KoniucJc, 
PI. IT, Pig. 14.. 
Slicll in shape an elongated cone ; the angle formed at tlie summit hy 
the median and vertical section of this cone is 10°. Septa snh-hemispherical 
with straight edges;* the distance between tliem is on the average three 
millimetres in a shell fifteen to twenty millimetres in diameter ; the last 
chamber does not seem to have been large. Siphuncle slender, central, not 
continuous, forming a small neck in each chamber. Test very thin. 
Dimensions. — Length, about thirteen millimetres ; diameter of the 
base, twenty-two millimetres. 
Relations and Differences . — This species differs from O. dimidiatum, 
Munster, in its small size and the lesser distance between the septa, as well as 
in the apical angle which is only G° in the species described by Count Munster. 
Horizon and Locality . — Elack argillaceous limestone of the Yass 
District. 
Observations . — Besides the species of Orthoceras I have just described, 
I have come across, among the specimens that have been submitted to me, 
several fragments of other species of the same genus, of which the state of 
preservation was too imperfect to enable me to determine them wdth certainty. 
One of this species seemed to me to bo near O. lineare, Munster, and is found 
in an argillaceous ferruginous conglomerate, composed of a large number of 
internal and external casts of various fossils ; the specimens of the others are 
rolled and distorted. I would add that although they have been collected in 
the Yass District, I would not venture to say that they come from the Devonian 
Eorniation. 
