W. S. Sudleston — On the Torkshire Oolites. 293 



ii. — contkibutions to the paleontology of the yorkshire 



Oolites. 



By Wilfrid H. Hudleston, M.A., F.E.S., F.G.S.] 



(Continued from Decade III. Vol. I. p. 252.) 



(PLATE IX.) 

 Genus Onustus, Humphrey, 1797. 



C1EVERAL trocliiform shells found in the Jurassic rocks, which 



were formerly referred either to Trochus or to Solarium, have 

 in more recent years been regarded as related to the genus Onustus. 



1 am not aware who was the first author to adopt this view, but we 

 find Hebert and Deslongchamps (1860) recognizing the genas in 

 the Callovian of Montr ueil Bellay. Subsequently Lycett (Suppl. to 

 the G-reat Ool. Moll. p. 103) gave a diagnosis, more especially as 

 applicable to the Jurassic species, and described Onustus Burtonensis 

 from the Forest Marble of Burton Bradstock. 



The Jurassic species referred to Onustus form a well-marked group 

 characterized by a wide-angled cone, made up of whorls which over- 

 lap so as to hide the suture ; the width exceeds the height ; the 

 ornamentation is longitudinal (axial) ; the base is nearly flat, as in 

 TrocJius, but with a convexity towards the centre. The Yorkshire 

 specimens, however, as far as can be seen, exhibit but small trace 

 of an umbilicus. Aperture depressed and very oblique. S. P. 

 "Woodward observes that shells extremely like the recent Phorus 

 (i.e. Onustus) are met with even in the Carboniferous Limestone. 

 In the Jurassic rocks of Yorkshire no specimens which could be 

 referred to Onustus have been found to my knowledge elsewhere 

 than in the Dogger.^ 



59. — Onustus ornatissimus, D'Orbigny. Plate IX. Fig. 1. 



1849. Trochus ornatissimus, D'Orbigny, Prod. i. p. 264 (Et. Bajocien). 



1852. „ ,, Terr. Jurass. ii. p. 272, pi. 312, figs. 5-8. 



Bibliograp'hy, etc. — D'Orbigny describes his species as of medium 

 size, and having a spiral angle of 85°. He distinguishes it from 

 *' TrocJius " heliacus and lamellosus principally through the character 

 of its ornamentation ; the longitudinal costge terminating in points, 

 which give to the periphery of the base a spinous aspect. 



Description. — Specimen from the Dogger (zone 1), Peak (Blue 

 Wyke). Leckenby Collection. 



Height 14 mniimetres. 



Widtli 21 „ 



Spiral angle 83°. 



The shell is trochiform, the spire being slightly hollowed out ; 

 base unseen. Whorls about 7 in number, excavated posteriorly and 

 overlapping sufficiently to hide the suture. The longitudinal costas 

 are but slightly developed in the anterior portion of the last two 



1 Some might be disposed to think that the fossils classed by Deslongchamps and 

 Lycett under Onustus present more resemblance to such modern genera as Calcar 

 and Uranilla. 



