ORTHOCERITID^. 
121 
sions of tlie body-chamber cannot be determined owing to its 
imperfect preservation. 
Bemarhs. The thinness and horny appearance of the test in this 
species is a feature which is met with in other forms in the Car- 
boniferous shales both in Britain and in Belgium, and probably 
denotes a deficiency in the supply of calcareous matter in the 
water which these species inhabited. 
Horizon. Calciferous Sandstone ^ ; Lower Limestone Group. 
Localities. Eskdale, Dumfriesshire ; Boghead, Lanarkshire ; 
Itedesdale, Xorthumberland ; Fifeshire. 
Some of the specimens from Redesdale were presented by J. E. 
Lee, Esq., E.S.A., E.G.S. 
This species is represented in the Collection by a large number of 
specimens. 
Orthoceras teres, Sowerby, sp. 
1821. Conularia teres, Sowerby, Mineral Conchology, voL iii. p. 108, 
tab. ccLv. if. 1, 2. [Not Orthoceras teres, Barrande, ante, p. 12.] 
Sp. Char. Shell very slightly curved. Section nearly circular, 
but a little compressed. Rate of tapering nearly 1 in 5. Septa 
somewhat distant, that is about 3- the diameter of the shell. Only 
three of the septa are visible, where the shell has been broken, at 
the apical end of the specimen. The siphuncle, which is seen only 
at the smaller extremity of the shell, is almost central. The sur- 
face of the test is beautifully ornamented with waved riblets, which 
form a deep sinus on the outer curvature of the shell, thence sweep- 
ing upwards in a broad arch on either side, and meeting in a very 
slight sinus on the opposite or inner curvature of the shell. About 
five of the riblets occupy the space of one line, the intervals between 
them being of about the same width as they. The apex, the tip of 
which is broken off, is quite smooth for a distance of about two 
lines, the riblets being at first crowded together, till at a height of 
The following is the succession of the rocks of the Carboniferous Limestone 
■Series of Scotland in descending order; — 
Carboniferous Limestone | Upper Limestone Group. 
Series 1 Coal Group. 
I Lower Limestone Group. 
Calciferous Sandstone i' Cement-stone Group. 
Series. f Red Sandstone Group, 
“ Tl)e Carboniferous Limestone Series of Scottish geologists probably repre- 
sents the upper part of the Carboniferous Limestone Series, or Yoredale Group 
of England.” (Dr. A. Geikie, ‘Text-Book of Geology,’ 1885, p. 739.) 
