W. R. Hudkston—On the Yorkshire Oolites. 201 



II. — Contributions to the Paleontology of the Yorkshire 



Oolites. 

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



(Continued from Decade III. Vol. II. p. 159.) 



(PLATE V.) 



Order Opisthobranchiata, Milne-Edwards. 



THE species belonging to this Order, which are enumerated below 

 and figured in the accompanying Plate, occur in the Lower 

 Oolites without exception. The Oxfordian beds in Yorkshire have 

 not been productive in fossils of this kind : the only known species — ■ 

 ActcBon retusiis, Phil. — has already been described in the " Coralliau 

 Gasteropoda" (Geol. Mag. 1881, p. 127, PL IV. Fig. 7). The 

 Tornatellid^ are the best represented, and especially Actceonina, but 

 none are numerous, and really good specimens, suitable for accurate 

 description, are rare indeed. 



Genus Acteonina, D'Orbigny, 1850 = Orthostoma, Deshayes. 



There has been some hesitation on the part of authors in accepting 

 D'Orbigny's name for this very important genus : accordingly we 

 find that Orthostoma was adopted by Buvignier and also by De Loriol 

 in his earlier works. But the latter author in 1874 finally accepted 

 D'Orbigny's generic name. Into the question of priority it is hardly 

 necessary to enter here : it is sufficient to mention that Orthostoma is 

 inapplicable, as having been used for another genus at an earlier date. 



The genus Actceormia is interesting to the paleeontologist as perhaps 

 the oldest member of theTornatellidae, dating from the Carboniferous 

 period. It is best represented in the Jurassic period, but failed con- 

 siderably during the Cretaceous. Stoliczka suggests that Aitriculina, 

 Gray, dredged in 63 fathoms, may be the modern representative of 

 Actceonina. According to D'Orbigny, the maximum development of 

 the genus was attained during the deposition of the Lower Lias. 

 Tate and Blake enumerate six species of Actceonina from the York- 

 shire Lias, but one of them must be referred to another genus. 

 Actceonina is singularly scarce in the Inferior Oolite of Dorset- 

 Somerset, and not a single species was quoted by Mr. Tawney in the 

 " Dundry Gasteropoda." The genus is better represented in the 

 Inferior Oolite of the Cotteswolds, and also in the Lincolnshire 

 Limestone. 



As originally constituted, this genus was made to comprehend the 

 so-called " Cones " of the Lias. The specimens described below are 

 all more or less turrited and would come within the following defini- 

 tion. " Shell turrited, or ovate, moderately thick, with more or less 

 elevated spire, inner lip flatly thickened at the edge, not plicated or 

 turrited, aperture evenly rounded in front ; the last whorl being 

 always anteriorly, somewhat suddenly contracted. The surface of 

 many Actceonince appears to be perfectly smooth, but it is more likely 

 this is only in consequence of the uppermost punctated layer of the 

 shell having been removed." ^ 



^ Stoliczka, Cretaceous Gasteropoda of Southern India, p. 399. 



