22 THE BRITISH CONULARLE. 



spicuous ; centre of face marked by a conspicuous longitudinal internal "septum." 

 Aperture slightly contracted; lobes broad and rounded; apex tapers to a sharp 

 point; apical septa unknown. Ornamentation highly characteristic. Ridges fine, 

 perfectly smooth, well spaced (5 — 6 in 5 mm.), forming an average angle of 132° 

 along the central rib. Furrows smooth or irregularly wrinkled. 



Dimensions. — Length at least 180 mm. Greatest width of face seen, 20 mm. 



Description. — It is certainly this species to which R. Etheridge refers, loc. cit., 

 but his specimens seem to have been very fragmentary, and he therefore gave no 

 name and no figure. Over seventy specimens have come under my notice, and the 

 species seems to be one of the best marked as well as one of the most interesting 

 known. At present it has only been found in the dark grey cement stone in the 

 Lower Carboniferous of Scotland, where it is always completely flattened. From the 

 equality of the faces, and the symmetry between the halves of each face, it may be 

 inferred that the cross-section was square. The most characteristic feature of the 

 shell is the strong median rib which is seen down the centre of each face. This 

 rib is of the same nature as the internal "septum" seen in C. aspersa, but as 

 the shells are always flattened, the rib becomes conspicuous upon the outer 

 surface. More often than not a complicated network is seen, for owing to the thin- 

 ness of the shell and the compression which has occurred, the transverse and longi- 

 tudinal ridges of the two under faces are also prominent upon the outer surface 

 (PL II, fig. 2). The ridges are smooth, glossy, and rounded, and are generally 

 well preserved. In the furrows the very thin shell is often seen to be wrinkled 

 (PI. II, fig. 3). 



The most remarkable feature of this species is the close association of several 

 individuals, which has not, to my knowledge, been recorded for any other species. 

 PI. II, fig. 1, shows at least sixteen specimens of varying sizes, attached at their 

 apices, and radiating from a centre. This is the most nearly perfect, though 

 not the only example, I have seen. In the British Museum (Nat. Hist.) is a slab 

 with three large specimens and a fourth fragment radiating from a centre (no. G. 

 17<>f>2) and another with at least seven small individuals showing radial arrange- 

 ment (no. 17664). There is no sign of specialisation among the individuals, and 

 the arrangement was, therefore, probably not of the nature of a true colony, but 

 merely an association of separate individuals. 



Affinities. — This species is quite unlike any other, owing to the thinness of the 

 shell, the central internal longitudinal rib, and the smoothness of the transverse 

 ridges. It is possibly allied to C. aspersa. 



Horizon and Localities. — Calciferous Sandstone : Glencartholm, Eskdale ; Water 

 of Leith ; Woodhall Mill. 



Type. — Geological Survey Museum, Edinburgh. 



