E. Wilson — British Liassic Gaderopoda. 199 



spaced from circumference to centre, or are much more distinct and 

 more widely spaced towards the circumference, in addition to the 

 radial serpentine lines and ridges above mentioned. Aperture trans- 

 verse, outer lip thin, with an irregular outline; inner lip concave, 

 with a broad expansion over the massive, axial and somewhat 

 obliquely produced columella. 



Dimensions. — Height, 10-75 millimetres; diameter, 9 mm.; length 

 of the last whorl, 6-75 mm. ; spiral angle, 60°; sutural angle, 125°. 



Note. — Figs. 5 and 5a, being drawn from a laterally compressed 

 specimen, show a rather greater breadth and spiral angle, and a more 

 transversely elongated aperture than this form really possesses. 



Affinities. — In its general form and ornamentation this shell 

 appears almost ideiitical with one (viz. fig. 6) of the figures of 

 D'Orbigny's Turbo subduplicatus (Pal. Fr, Terr. Jur. vol. ii. p. 339, 

 pi. 329, figs. 1-6), a species which, according to that authority, 

 is synonymous with Trochus duplicatiis , Sow., Turbo duplicatus, 

 Goldfuss, Turbo plica tus, Goldfuss, and Turbo Palinurus, D'Orb. We 

 are, however, confronted with the fact that the Northamptonshire 

 fossil is certainly not a Turbo, but a Trochus. 



The aperture of the particular form {I.e. pi. 329, fig. 6) which 

 is so like our specimens is not shown, but the author defines its 

 character in this very variable species of his as " round, with a broad 

 thickening over the columella." The question arises, was the aperture 

 of this particular shell {I.e. pi. 329, fig. 6) hidden or imperfectly 

 shown, and has D'Urbigny mistaken its genus in consequence, or has 

 he and Goldfuss also (Petr. Germ. vol. iii. p. 95, pi. 179, fig. 2) mis- 

 interpreted the character of this portion of these shells generally, 

 and thus of the genus, from having had to deal with imperfectly- 

 preserved specimens ? ^ The description and figure of Trochus 

 duplicatus, Sow., which give the aperture as quadrangular (Min. 

 Conch, vol. iii. p. 181, t. 181, fig. 5), indicate that Sowerby's type 

 was a genuine Trochus. The species Trochus duplicatus. Sow., is 

 therefore good, and must stand. If Goldfuss and D'Orbigny were 

 correct in their respective specific identifications of Turbo duplicatus, 

 and Turbo subduplicatus, with Sowerby's type, they have both erred 

 in their generic appellation. However this may be, I consider the 

 Northampton fossil distinct from all these, with the probable exception 

 of the particular shell figured by D'Orbigny as Turbo subduplicatus 

 {I.e. pi. 329, fig. 6), which — relying upon the vertically truncated 

 whorls and spiuose and widely-channelled double-keel — I consider 

 distinct from the other forms figured by that author {I.e. pi. 329, 

 figs. 1-5). 



Geological Position and Locality. — Upper Lias, zone of Am. 

 communis, New Kailwaj', Weedon and Dodford, near Daventry, 

 Northamptonshire. 



1 The matter is complicated by D'Orbigny describing a tj-pical Trochus duplicatus, 

 Sow., in another part of the Pal. Franc. (Terr. Jur. Gast. ii.p. 275, pi. 313, figs. 5-8) 

 under that name. 



