EXPLANATION OF THE PLATES AND WOOD-CUTS. 



This is the internal cast of a shell of a very unusual form, — we have referred it 

 to Montfort'^ genus Polyphemus, as bearing the nearest resemblance to it of any 

 we know. The curvature is possibly the effect of fracture. 



Plate XL. 



Fig. 1. Trochusl Usocona. Conical, with a broad base, marked with obscure concen- 

 tric ridges ; whorls about 5, their upper parts convex, the lower concave, with a 

 broad band in the hollow ; edge of the base obtuse. 

 Height 2 inches, diameter nearly o inches. 



The broad band around this shell would lead us to place it as a Pleurotomaria, 

 did the lines of growth indicate that there ever was a deep sinus in the edge of 

 the aperture. 

 Fig. 2. Conularia quadrisulcata, (M. C. t. 260. f. 3— G. Siltir. Sijst. p. 626. PI. 

 XIL f.) 



Many of the specimens in ironstone have smooth furrows between the crenated 

 ridges, as shown at fig. 2 a., in others the furrows are crossed by striae, as at fig. 

 2 b., and both these forms may sometimes be found in one specimen, and arise 

 from the presence or absence of a thin, dai'k brown skin or covering, the interior 

 of which is smooth and the exterior wrinkled ; the ridges are often denticulated or 

 notched. See ante, p. 442. 

 Fig. 3. Orthoceras scalpratum. Lanceolate, compressed, smooth, slightly curved, 

 with the edges angular, the inner one sharp ; septa numerous ; siphuncle small, 

 near the obtuse edge. 

 Diameter 1^ inch. 

 Fig. 4. Represents the interior of a small Orthoceras with numerous septa, and a 



nearly marginal siphuncle. 

 Fig. 5. 5 a. and 5 b. Nautilus cUtellarius. Globose, umbilicated, septa numerous, much 

 bent in the middle, truncated and not recurved at the ends ; siphuncle central ; 

 umbilicus small, cylindrical ; aperture above twice as wide as long. 



The length of the aperture is li inch, the width 2| inches. Diameter of the 

 shell 2f inches. 



Fig. 5. A front view of a specimen in which only a few chambers have been filled 

 with ironstone, and it may be remarked that most of the specimens are preserved 

 in the same manner. The whole of the shell has decayed away, and with it all the 

 inner whorls have disappeared : the ironstone not having entered them, that por- 

 tion of the ironstone which fijled the umbilicus wanting support has been subse- 

 quently broken and pressed into the cavity left by the shell. Fig. 5 a. is a lateral 

 view of a similar specimen. Fig. 5 b. shows the remarkable curvature of the septa. 

 Fig. 6. Nautilus concavus. Subglobose, umbilicated, concave on the front; septa 

 shghtly arched ; siphuncle central ; umbilicus large ; aperture nearly twice as 

 wide as long. 



Length of the aperture 7 lines, width 1 inch. 

 Diameter of the shell 1 inch 1 lines. 



