﻿146 BRITISH FOSSIL CEPHALOPODA. 



Orthoceras subgregarium, M'Coy, PL XII. fig. 6. 



1846. Orthoceras subgregarium, M'Coy, 'Sil. Foss. of Ireland,' pi. 1, fig. 4, p. 9. 



Type. — I have not been able to discover this among the others in Sir R. 

 G-riffiths's collection in the Royal Dublin Museum, but the author's figure and 

 description are very definite. The section is elliptic, the diameters being as 5 to 4. 

 The rate of increase of the longer diameter is 1 in 18. The whole is septate, and the 

 surface is not seen. The septa are direct, and have a medium convexity equal to 

 the distance of the sutures, which is about ^ the long diameter. The siphuncle 

 is on the short diameter, -| of that line from the side. It is too large to be called 

 filiform. The greatest diameter is ^ inch, and the length is 1^ inches. From the 

 Bala quartzites, Cong. 



General Description. — Some fossils from the same series in Ireland and elsewhere 

 may perhaps be referred to this type. The section is either circular, or has axes in 

 the ratio of 7 to 6. Some slight curvature is seen in one example. The rate of 

 increase of the long diameter varies between 1 in 15 and 1 in 19. One shows a 

 body-chamber of 2^ inches, which is more than twice the basal diameter, and the 

 aperture, which has no constriction beneath it, has an undulating outline. There 

 are only obsolete and oblique lines of growth. The septa are slightly oblique in a 

 direction opposite to the slope of the aperture, and have a moderate convexity. 

 Their distance is from \ to ^ the diameter. In the case of the example showing the 

 aperture, only the two last septa are seen, which may be closer than the rest. The 

 siphuncle is situated from f- to \ the diameter from the side, and when the axes are 

 unequal lies on the shorter. Its diameter is \ of the whole, and its elements are 

 cylindrical. The largest diameter is more than 1 inch, and the greatest length 

 2-^ inches. 



The identification of this species is not a very satisfactory one, as the examples 

 seen give the characters separately, and none unites them all. 



Relations. — There is nothing to distinguish some of these from 0. politum except 

 the distance of the septa ; the figured specimen indeed might belong to the latter 

 species, if it were proved that in it the last two chambers were only half as deep as 

 the rest.- 



Distribution. — In the Upper Arenig of St. David's ? (1) ; in the Bala Series of 

 Bala (3), and of Kildare (1) ; in the Upper Llandovery of Boocaun (1), of Llan- 

 dovery (1), and Coldbrook (1), and perhaps in the Shales of Kirkcudbright Bay (1). 

 This species is recorded also by Kelly from Leenane, Munterowen, and Ardaun ; 

 also by Baily, as from the Upper Llandovery of Cong, and the Bala Limestone of 

 the Chair of Kildare; and in the Catalogue of Western Scottish Fossils, from 

 Drummuck. 



