15 



DESCRIPTION OF A NAUTILOID, PLEURONAUTILUS FULCHER, 

 N.sp., FROM THE CARBONIFEROUS ROCKS OF ENGLAND. 



By G. C. Crick, F.G.S., 



Of the British Museum (jS"atural History). 



Read llth December, 1903. 



PLATE II. 



The new species, Pleuronautilus pidcher, described in the present 

 paper is based upon four examples and a fragment ; of these, two and 

 the fragment are in the British Museum collection, the others in the 

 collection of Dr. Wheelton Hind, of 8toke-upon-Trent. 



It may be characterized as follows : — Shell small, evolute, with the 

 aperture only just in contact with the preceding whorl, thick- discoid, 

 rapidly increasing in diameter, and having a central vacuity ; greatest 

 thickness at about the middle of the lateral ai'ea, from six- to seven- 

 elevenths of the diameter of the shell ; height of outer whorl from 

 about four-elevenths to two-fifths of the diameter of the shell. 

 Whorls two in number ; inclusion very slight, but apparent at the 

 completion of the first whorl ; umbilicus deep, exposing the inner 

 "whorl, with steep sides and convex margin, from about two-fifths to 

 about one-third of the diameter of the shell in width, and having 

 a central vacuity. Whorl depressed elliptical or sub-tetragonal in 

 cross- section, rather wider than high ; scarcely indented b)^ the pre- 

 ceding whorl; periphery broad, feebly convex, somewhat flattened in 

 the centre and bevelled or even slightly concave on each side, separated 

 from each lateral area by a narrow well-marked zone (the lateral 

 ventral zone) ; sides rather narrow, somewhat flattened and divergent ; 

 umbilical shoulder rounded, ill-defined; inner area (or umbilical zone) 

 convex, not sharply defined. Body-chamber occupying fully half of 

 a whorl; aperture not seen, but, judging from the ornaments of the 

 test, with a feeble sinus on the lateral area and a broad deep 

 hyponomic sinus on the periphery. Chambers (camerse) not very 

 shallow, being near the base of the body-chamber about one-third of 

 the height of the whorl in depth ; suture-line with a feeble sinus on 

 the lateral area, a broad shallow sinus on the periphery, and a small 

 distinct dorsal or internal lobe. Siph uncle small, about two-fifths of 

 the height of the whorl below the periphery apparently at all stages 

 of growth. Test rather thick and beautifully ornamented ; at about 

 the end of the first half-whorl the shell becomes somewhat suddenly 

 swollen, and two distinct longitudinal parallel ridges originate on 

 each side of the peripheral area, the outer one on each side 

 coinciding with the boundary of that area, and limit a distinct ' lateral 

 ventral zone,' which is clearlj- defined almost to the aperture of the 

 shell ; at the same place there appear on the lateral area of the whorl 

 feeble, broad, somewhat forwardly-inclined folds which become very 

 prominent, forming almost a node, at the raised lateral margin of the 

 lateral ventral zone ; these folds soon assume the form of distinct 



