﻿BRITISH FOSSIL CEPHALOPODA. 169 



Cyrtoceras macrum, Blake, PL XX. fig. 3. 



Type. — Section elliptical, with diameters in the ratio of 7 to 6, the long diameter 

 in the plane of curvature ; mean radius of curvature 19 lines. The long diameter 

 increases at the rate of I in 7, measured along the convexity. No surface is seen, 

 and all is septate. The septa have a convexity of about i the diameter. They are 

 very close at ^ the mean diameter apart. Sutures sigmoidal rather than concave, 

 the more convex part on the inside, a little oblique, rising to the convex side. The 

 siphuncle is not clearly seen, but it may be small and internal. From the Bala 

 Beds, Rhiwlas, Bala. In the Museum of Practical Geology. 



General Description. — This cannot be considered a satisfactorily determined 

 species, as two very important points of its diagnosis are wanting — the surface and 

 the true position of the siphuncle. It is, I think, distinct from Cyrtoceras plebeium, 

 though closely allied. It is stouter, has less curvature, and a slower rate of increase 

 with more sigmoid sutures. Of course, if the siphuncle be internal, the distinction 

 is complete. 



Distribution. — In the Bala Beds, Rhiwlas (1). 



Cyrtoceras reversum, Blake, PI. XXI. fig. 5. 



Type. — Section doubtful, as the specimen is compressed in the shale. It appears 

 now to be elliptic, with diameters in the ratio of 18 to 11, the long diameter being 

 in the plane of curvature. External mean radius of curvature, 3£ inches ; hence the 

 curve is slight. The long diameter increases at the rate of 1 in less than 3. The 

 surface at present is smooth, but the outer layer of the shell is not seen. The whole 

 is septate, and the septa are about \ the long diameter apart. The great peculiarity 

 of the species lies in its sutures, which, instead of being concave forwards and 

 nearer the aperture on the outside as usual, curve gently backwards, and are thus 

 oblique and convex to the aperture. The siphuncle is not certainly seen, but seems 

 to be internal. Length, 19^ lines ; greatest diameter, 1 inch. From the Lower 

 Ludlow, Ledbury. In the collection of Dr. Grindrod. 



General Description. — The type is unique. 



Relations. — The remarkable character of the sutures separates this species from 

 all others except C. incequiseptum, which is a much stouter form, and even in that 

 the character is not so marked. 



Distribution. — In the Lower Ludlow, Ledbury (1). 



