380 GASTEROPODA OF THE INFERIOR OOLITE. 



817. Trochus monilitectus, Phillips, 1829. Plate XXXII, figs. 3 a, 3 b. 



1829 and 1835. Trochus monilitectus, Bean, MS. Phillips, Geol. Yorks., pt. 1, p. 152 



(3rd edit., p. 259), pi. ix, fig. 33. 



1850. — — Phil. d'Orbigny, Prod., 1, p. 265. 



1851. — — — Morris and Lycett, Great Ool. Moll., pt. 1, 



p. 116, pi. xv, fig. 1. 

 1885. — — — Hudleston, Geol. Mag., dec. 3, vol. ii, 



p. 121, pi. iii, figs. 1, la, lb. 

 Cf. also — Brutus, d'Orbigny. Terr. Jur., vol. ii, p. 283, pi. cccxv, 



figs. 13—16. 

 — — Cossmann, Etage Bath., p. 285, pi. vii, 



figs. 23—24. 



Bibliography, 8fc. — This little shell is a genuine representative of the section 

 Zizyphinus, and belongs to a group completely conical in outline, the result of flat 

 whorls and a close suture. In the Bathonian of France Trochus Zenobius, d'Orb., 

 seems to represent it. Trochus Brutus, which has a wider spiral angle, is stated by 

 M. Cossmann, on the authority of Schlumberger, to be common in the Bajocian, 

 I presume of eastern France. 



Description. — Typical form from the Scarborough Limestone of Cloughton 

 Wyke: 



Height . . . . .8 mm. 



Width ..... 7-5 mm. 



Spiral angle ..... 60°. 



Shell regularly conical, imperforate ; spire acute, and nearly two-thirds the 

 total height. Whorls flat, suture extremely close. The ornaments consist of 

 four, and sometimes five equal spiral bands, which are close together and evenly 

 tuberculated, the tubercles or granules being nearly circular. 



The body-whorl has four tuberculated spirals, together with a thicker belt, 

 constituting the basal periphery. Base flat with faint spiral stria3 towards the 

 margin (not always visible), the rest smooth or only marked by faint radial lines. 

 Aperture rhomboidal and depressed. 



Relations and Distribution. — The typical T. monilitectus seems almost confined 

 to the Scarborough Limestone and to the Upper Beds of the Lincolnshire 

 Limestone, especially at Ponton, where its presence was first recorded by Morris 

 in 1853 (' Quart. Journ. Geol. Soc.,' vol. ix, p. 326). 



Further south, e. g. in the Parkinsoni-zone of Aston, Notgrove, and Horton Hill, 

 and also at Grove, near Castle Cary in Somersetshire, there occurs a larger form 

 with five or six nodular spirals (see fig. 4). The greater number of spirals is often 



