104 I*yof. Nicholson — On Endoceras in Britain. 



the longitudinal striae are nearly or quite as well marked as the 

 transverse ones. The longitudinal striee are about eighty in the 

 space of an inch, and are, therefore, not so closely approximated as 

 are the transverse strias. The result of this is, that the spaces in- 

 cluded between the two sets of striae are oblong in the parts occupied 

 by the crowded fascise of transverse striae, whilst they become nearly 

 square in the interspaces between these fasciae. Independently of the 

 transverse striae, the surface of the shell is marked by numerous 

 slightly elevated transverse ridges or annulations, which are placed 

 at no constant distance from one another, and which do not, there- 

 fore, mark the position of septa in the shell. 



In the absence of any traces of septa or of a siphuncle, it may seem 

 somewhat hazardous to refer our fossil to Endoceras ; but the nature 

 of the surface-marking is so characteristic, that I feel no hesitation 

 in determining it to be a young specimen of Endoceras proteifoi-me, 

 Hall. The following is the description given by Hall of this species 

 (Pal. N.Y., vol. i., p. 208) :— 



" General form cylindrico-conical, more or less elongated, often 

 compressed, tapering somewhat unequally in different specimens ; 

 young specimens terminating in an extremely acute point ; surface 

 marked with distinct transverse striee, which usually appear like 

 narrow sub-imbricating bands, with one edge well defined and more 

 elevated than the other, more or less distinctly striated longitudi- 

 nally; strise varying from extreme tenuity to distinct elevated thread- 

 like lines ; section circular ; septa distant from one-fifth to one- 

 fourth the diameter; siphuncle excentric or submarginal." The 

 siphuncle in old specimens usually contains " a smooth cylindrico- 

 conical embryo-tube or sheath," within which are young shells, 

 which may or may not possess septa and a siphuncle, but which are 

 distinguished by their surface-marking from the perfectly smooth en- 

 veloping tube. 



Hall distinguishes three chief varieties of this species. 



1. E. proteiforme, var. tenuistriatum, having the transverse strise 

 much more conspicuous than the longitudinal stri^, and often arranged 

 in fascise. 



2. E. proteiforme, var. tenuitextum, very similar to the preceding, 

 but having the striee of both sets more nearly alike and equal, being 

 also " more distinctly elevated and thread-like." 



3. E. proteiforme, var. Uneolatum, having numerous delicate trans- 

 verse striae, arranged in fasciae, but having no longitudinal stri^ in 

 the majority of instances. 



The first two of these varieties hardly appear to be distinct, but 

 upon the whole our specimen agrees most closely with the second of 

 these. I regard it, therefore, as being a young form of Endoceras 

 proteiforme, var. tenuitextum, Hall. Its locality is Skelgill Beck, near 

 Ambleside, in the black Graptolitic Mudstones of the Coniston Series, 

 immediately above the Coniston Limestone ; and it is, therefore, of 

 later age than the American examples of the species. 



