POTERIOCERAS. 115 



but it is distinguishable by its more regular contour and the great obliquity of its 

 septa. G. lumbosum, Barrande,^ another neighbouring form, is more evenly convex 

 ventrally, and is more constricted round the aperture. C. reductum, Barrande/ is 

 much slighter and more elongate, and has a smaller body-chamber. 



3. POTERIOCBEAS ELLIPSOIDEUM (Phil.). PI. XI, figS. 1, 1 a, 1 h. 



1841. Oethoceeas ellipsoideum ?, Phil. Pal. Foss., p. 140, pi. Ix, fig. 205*. 



1841. — vENTEicosxTM, Phil. Ibid., p. 230. 



1842. Orthoceeatites subpteifoemis, D'Arch. and de Fern, (not Munsier). 



Geol. Trans., ser. 2, vol. vi, pt. 2, p. 

 347, pi. xxviii, figs. 3, 3 a. 



Descri'ptioti. — Shell small, almost straight, tapering. Ventral, dorsal, and lateral 

 outlines gently convex on the body-chamber, becoming straight on the septal part, 

 except the dorsal outline, which is on that part very slightly concave. Section 

 very ellipsoidal, with the dorso-ventral to the transverse diameter in the ratio of 

 4 : 5, the ventral side being somewhat flattened, so that the ellipse is not exact. 

 Body-chamber apparently rather deep and considerably narrowed in its lower 

 portion. Septa almost flat, rather broad, being distant about one-eighth their 

 height, but becoming closer below. Siphuncle close to the ventral side. Surface 

 unknown. 



Size. — Height, 30 mm. ; dorso-ventral diameter, 21 mm. in greatest width ; 

 lateral diameter about 25 mm. 



Locality. — Wolborough. Two specimens in the Museum of Practical Geology. 



Bemarhs. — The specimen from which the above description is taken is fairly 

 distinct, but the other, though rather larger, is very poor and indefinite. I am in 

 doubt as to whether it belongs to this species or to Ph. vasiforme, but the flattened 

 back and general curvature incline me, on the whole, to class it with this one. 



Phillips's figure and description of this species are very slight, and for a long 

 time I felt unable to identify with it any of the Newton specimens which I knew. 



A comparison, however, of his figure with fig. 1 a of the Jermyn-Street 

 specimen shows the greatest similarity, both in general shape and in septal 

 width. Hence I conclude that Phillips drew his fossil, not, as might have been 

 supposed, in a ventral, but in an oblique, almost lateral, position, being probably 

 led to do this from that being the best view of a defective specimen. We may, 

 therefore, regard our figures as representing the shape of his species. 



1 1877, Barrande, ' Syst. Sil. Boheme,' vol. ii, Suppt., p. 33, pi. cccclxiv, figs. 1, 2 ; pi. cccclxv, 

 fig. 1, and pi. cccelxx, figs. 1 — 3, fit. Gr. 



2 Ibid., p. 42, pi. cccclxxii, figs. 1—4, £t. G. 



