150 EOCENE MOLLUSCA. 



No. 89. Voluta ambigua. Solander. Tab. XIX, figs. 4, a — c. 



Stkombus ambiguus, Soland. 1766. Brand. Foss. Hant., p. 32 ; t. 5, fig. 69. 

 Voltjta btcorona, Webster. 1814. Geol. Tran., 1st Ser., vol. ii, p. 204. 

 — ambigua, Sowerby. 1823. Min. Con., vol. iv, p. 135; t. 399, fig. 1. 

 Nee — — Lamk. 1811. Ann. du Mus., vol. xvii, p. 78, No. 12. 



nee — — lb. 1822. Hist, natur., &c., vol.x, p. 352, No. 12. 



nee — — Besh. 1824-37. Desc. des coq. foss., vol. ii, p. 691 ; t. 93, figs. 10, 11. 



nee — — (Var. Monstrosa) Sow. 1816. Min. Con., vol. ii, p. 31 ft. 115, fig. 5. 



nee — — Mant. 1822. Foss. of the S. Downs, p. 108 ; t. 18, fig. 8. 



nee — — Grat. 1845. Conchyl. foss., &c., de l'Adour, t. 1, figs. 14, 15. 



nee — — Rouault. 1850. Desc. des foss., &c., de Pau. (Mem. de la Soc. Geol.de 



France, 2d ser., vol. iii, p. 457 ; t. 18, figs. 15, 16.) 

 nee — — D' Arch. 1850. Desc. des foss. du groupe Nummul. (Mem. de la Soc. 



Geol. de France, 2d ser., vol. iii, p. 447.) 



V. testa ovato-oblongd, costettatd, transversim sulcata, ad basin emarginatd ; spird 

 conicd, elevatd, ajoice acuto .- anfractibus convexis, per-obtuse angulatis j costettis nwnerosis, 

 irregularibus, tuber cutis per-minuiis, acutis, terminantibus : aperturd postice sub-canaliculatd, 

 angustatd, in medio effusd; labro intus incrassato, plicalo, ad marginem crenulato ; colu- 

 mella sub-redd, rotundatd, bis vet ter plicatd. 



Var. compressa testa costatd; anfractibus angulatis; costis pro-eminentibus, sub-dis- 

 tantibus, compressis, tuberculis nodiformibus coronatis. 



Shell ovately oblong, longitudinally ribbed, transversely furrowed, widely, not deeply 

 notched in front ; spire conical, elevated, pointed ; whorls convex, scarcely angulated 

 at the shoulder ; ribs numerous, irregular, slender, extending nearly to the base of the 

 shell, and terminating above in a single row of very small spines or pointed tubercles ; 

 in the young state a second row of imperfect spines runs round the whorl near the 

 suture, but disappears as the shell is matured. The space between the suture and the 

 row of tubercles is nearly flat, and presents a slender, but prominent, raised line run- 

 ning along the middle, and sometimes an additional faint one on each side of the centre 

 line. The furrows are rather numerous, irregular, and traversed by very fine, but con- 

 spicuous, lines of growth. The aperture is contracted at the posterior extremity, 

 effuse at the middle ; the outer lip much thickened, plicated within, and crenulated on 

 the edge ; the columella round, straight, and furnished with two nearly equal prominent 

 oblique folds in front, and sometimes one or two obscure ones behind. 



The rounded shoulders, convex whorls, and conical spire, impart to this Volute a 

 regularity of form which distinguishes it from all its congeners. The margins of the 

 mantle of the animal appear to have been capable of considerable extension, for the 

 porcellanous matter deposited is occasionally found widely spread, covering the whole 



