CARBONIFEROUS LIMESTONE FOSSILS. 265 



Very rare in the carboniferous limestone of Lowick, North- 

 umberland. 



{Col. University of Cambridge.) 



Orthoceras (i Poterioceras) cornu-vaccinum (M'Coy). 



Desc. Conical, rapidly tapering to an obtusely rounded point, 

 very slightly arched ; section perfectly circular throughout ; 

 septa very oblique, flattened, sHghtly convex, moderately ap- 

 proximate, extending much further forward on the inner side 

 of the general curve than on the outer or convex aspect, the 

 lateral edges being very slightly sigmoidal, on account of their 

 obliquity ; the septa are broad oval in form, the longest dia- 

 meter being in the antero-posterior direction; siphon large^ 

 about its own diameter within the outer edge (corresponding 

 with the convexity of the general curve of the shell). Surface 

 horny in appearance, marked with irregular scratch-like lon- 

 gitudinal markings, and fine, nearly regular transverse im- 

 pressed lines, separated by rather wider flattened spaces; 

 thirteen transverse strise in 2 lines at an inch and a quarter 

 in diameter, about twenty in the same space at 9 lines in dia- 

 meter. Length of average specimen 5 inches 9 lines ; 2 inches 

 3 lines in diameter at the anterior end, and regularly tapering 

 to the obtusely pointed apex in the above length ; average 

 distance of the last few septa 2 lines. 



The above measurements are of average-sized specimens, 

 although examples occasionally occur a couple of inches long. 

 The general, slightly curved, obtusely pointed, rapidly tapering 

 form, and peculiar horny looking texture have suggested the 

 specific name. The only described fossil it has any resemblance 

 to is the Cijrtoceras Verneuilanum of De Koninck (A. F. B. t. 48. 

 f. 6), but it is easily distinguished by that species having a broad 

 oval transverse section, while the section of the present fossil is 

 perfectly circular ; and the septa, which from their obliquity ap- 

 pear oval, have their long axis directed in the opposite direction ; 

 the curvature is also less in our fossil. Some of the specimens 

 show a very slight contraction at the mouth, which renders it 

 probable that the species belongs to the subgenus Poterioceras, 

 with which all the other characters agree exactly and better than 

 with any other section of Orthoceras. 



Not very uncommon in the carboniferous limestone of Lowdck, 

 Northumberland. 



{Col. University of Cambridge.) 



