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GASTEROPODA OF THE INFERIOR OOLITE. 



The aperture in the early stage is very like Purpnrina, the anterior cana- 

 liculation being well marked. This feature is also seen in the middle stage, but 

 disappears more or less completely in the big shells, where the mouth is sub- 

 circular, the shape of the aperture being materially modified, with considerable 

 thickening of the inner lip (see especially PI. XXI, figs. 16, 17, and 18). 



Varieties. — The specimens from the type locality are of medium size. 

 PI. XXI, fig. 13, is probably one of Sowerby's types with the tuberculations worn 

 off the spiral ridges, and the cross-hatchings almost obliterated by usage. 

 Fig. 14 from the same locality is in very fair preservation, and probably shows 

 the true character of the type form. The cross-hatchings are wide and coarse, 

 the posterior spiral is very close to the suture, and there is some tendency to 

 tuberculation on the spirals in the base of the body-whorl. 



The variety spinulosa, Miinst., PI. XXI, fig. 15, which I consider synonymous 

 with Parpurina Bathis, d'Orbigny, is a large, handsome, and richly ornamented 

 form, which occurs rarely in the Goncavus-hed at Bradford Abbas. 



The variety to which I have given the name abbas, PI. XXI, figs. 16, 17, 18, 

 and PI. XXII, fig. 1, is extremely common on the same horizon and at the same 

 place. From well-preserved specimens of this most abundant form we gather 

 that, although the spire is pointed on the whole, yet the apex is obtuse ; the 

 earlier whorls are extremely angular, and the third spiral is seen to be developed 

 at a very early stage, already receding and less prominent than the others. In 

 the more mature whorls of this variety the crenulations or tuberculations on 

 the spirals become very faint, and in the very large shells disappear altogether. 

 On the whole the var. abbas is rather more slim in shape and more delicate in 

 ornamentation, though attaining to a much greater size than the type variety. 



Relations and Distribution. — We may well regard this as nothing more than a 

 modified descendant, on a higher horizon, of Amb. capitanea. Besides the 

 differences already indicated, it may be worth while to point out that the spirals 

 in the case of Amberleya ornata are but slightly tuberculated as compared with 

 those of Amb. capitanea. 



In Dorsetshire Amb. ornata is essentially a fossil of the Concavus-zone, and is 

 probably the most abundant fossil on that horizon at Bradford Abbas. At 

 Dundry one cannot say on what horizon it occurs, but probably below the Hum- 

 pltrirsianus-zone. It is rare in the Cotteswolds, where specimens are usually small 

 aud poorly preserved. Small forms of Amb. ornata, showing a slight tendency to 

 produce an intermediate keel in the body-whorl, occur towards the base of the 

 Inferior Oolite at Lincoln. There are also small Sf)ecimens in the Dogger at 

 Blue Wyke, which may either be immature forms of Amb. ornata or varieties of 

 Littorina (Turbo) Phillipsii. 



