122 
NAUTILOIDEA. 
about two lines above tbe smooth area they assume their ordinary 
size and spacing. The dimensions of the type specimen are : — 
Length 16 lines, greatest diameter 6 lines, least diameter 2 lines. 
Remarhs. Mr. John Young, of the Hunterian Museum, Glasgow, 
writes to me concerning this species as follows : — “ The fossil 
named by Sowerby Conularia teres is what we now term Orthoceras 
subcentrale, de Kon.^ At one time it was identified as Orthoceras 
sulcatulum^ M‘Coy but de Koninck, on one of his visits to Glasgow, 
claimed it as his species.” 
Having Sowerby’s shell before me, I find myself unable to identify 
it either with M‘Coy’s or with de Koninck’s species. From the 
former it differs entirely by the much greater regularity of its 
ornaments, and from the latter by their being distinctly and 
strongly waved ; whereas from what I can judge from de Koninck’s 
description and figure of 0. subcentrale that species has nearly if 
not quite direct riblets. Moreover, it has an eccentric siphuncle, 
and that organ is nearly central in 0. teres, though one cannot 
place much reliance on this point, because the siphuncle is apt 
sometimes to change its position with the growth of the shell. 
However, I think that the present form is distinct from those above 
named. 
A group of species of Orthoceras will be found on plates cccv. 
and cccvi. of Barrande’s Syst. Sil. de la Boheme, which resemble 
the present species in the markedly sinuous character of their orna- 
ments, and some of them (0. curtum, e. g.) in their short, conical 
form, but none of them approach 0. teres sufficiently closely to 
suggest specific identity with it. Barrande’s species belong to his 
Etages D and E (Silurian), the majority of them to the latter 
division. 
Horizon. Upper Limestone Group 
Locality. Thornliebank near Glasgow. 
Bepresented by the type specimen contained in the “ Sowerby 
Collection ” in this Museum. 
‘ Descrip, des Anim. Fossiles dans le Terrain Carbonifere de Belgique, p. 514, 
pi. xliv. f. 3, a, h (1844). 
2 Synop. of the Carboniferous Limestone Fossils of Ireland, p. 8, pi. i. f. 4 
(1844). 
^ Carboniferous Limestone Series (see footnote, p. 121). 
^ This is written “ Tronlie Bank ” by Sowerby {loc. cit.). It is recorded under 
the heading “ Thornliebank District ” in the ‘ Catalogue of Western Scottish 
Fossils,’ p. 91. 
