330 GASTEROPODA OF THE INFERIOR OOLITE. 



Bibliography, Sfc. — The author recognised a form of Onustus, occurring rarely 

 at Balin and Sanka, which he regarded as occupying an intermediate position 

 between 0. ornatissimus, d'Orbigny, and 0. papyraceus, Heb. and Desl., the latter 

 representing the section of which 0. pyramidatus is the type. 



Description .- 



Height . . . . .10 mm. 



Width . . . . .12 mm. 



Spiral angle ..... 68°. 



Shell short, conical, pointed. The spiral angle but slightly concave. Number 

 of whorls about six. These are flat, closely fitting, and ornamented with very 

 regular costse of moderate prominence, so arranged that there are about thirty in 

 the body-whorl. The intercostal spaces are moderately scaly. 



Base nearly flat, but rising towards the rhomboidal aperture ; peripheral border 

 slightly crenulated. There is a very faint submarginal channel, and an umbilical 

 hollow rather than a true umbilicus : spiral strise of the base very distinct. 



Relations a.nd Distribution. — Although this shell does not correspond in all 

 respects with the form described by Laube, its obviously intermediate character 

 between the pyramidatus-group and 0. ornatissimus must be my justification 

 for thus identifying it. Whilst the flanks of the shell are characteristic of 0. 

 pyramidatus and its allies, though with a narrower spiral angle, the spiral 

 ornamentation of the base entirely removes it from this group, and brings it into 

 comparison with the still stronger basal strias of the species next described. 



A single specimen from Stoford, horizon unknown. Fig. 7, representing a 

 shell from the Cadomensis-bed, Oborne, may be a variety. 



264. Onustus ornatissimus, d'Orbigny, 1850. Plate XXVII, figs. 8 a, 8 b. 



1850. Trochus ornatissimus, d'Orbigny. Prod., i, p. 264. 



1852. — — — Terr. Jur., vol. ii, p. 272, pi. cccxii, 



figs. 5—8. 

 Cf. also — — — ?, var. Poktonis. Morris, Quart. 



Journ. Geol. Soc, vol. ix, p. 343, 

 pi. xiv, fig. 10. 

 Non Onustus ornatissimus, d'Orb., sp. Hudleston, Geol. Mag., dec. 3, vol. i, 



p. 293, pi. ix, fig. 1. 



Description : 



Height of average specimen . . . 10 — 12 mm. 



Width ..... 17—19 mm. 



Spiral angle (concave) . .' . . 80° — 85°. 



