﻿AMBERLEYA. 



285 



215. Amberleya Orbignyana, sp. nov. Plate XXII, figs. 7, 8. 



. Purpurina ornata, d'Orbigny. Terr. Jur., vol. ii, pi. cccsxx, figs. 4, 5. 



Bibliography, Sfc. — There is no reference to Purpurina ornatam the text of the 

 4 Terrains Jnrassiques,' though we gather from the explanation to the plate that 

 it is a fossil of the Inferior Oolite. Purpurina ornata is evidently an Amberleya 

 (Eucyclus), and we at once recognise the form as common and characteristic of the 

 Parkinsoni-zone of Dorset. The specific name " ornata " being preoccupied, it 

 becomes necessary to bestow on this fossil a fresh appellation. 



Description : 



Length of well-grown specimens . . 35 — 45 mm. 



Length of body-whorl to total height . . 50 : 100. 



Spiral angle .... 45°. 



Shell eucycloid, turrited. Whorls nine or ten, angular, and sloping flatly 

 towards the dominating keel. The whorls of the spire are biangulated anteriorly; 

 a faintly nodular spiral is developed close to the upper suture, then ensues the 

 flat sloping area, marked by extremely fine strias rather oblique to the axis ; the 

 two principal keels or spirals are quite low down, the upper one having large 

 tubercles, wide apart and spirally extended ; in the lower keel the ornaments are 

 usually less conspicuous. 



The body-whorl is large, very angular, with the great keel strongly tuber- 

 culated ; there are five spirals in the base, these being slightly tuberculated. The 

 aperture is ovate-elongate, with a straight columellar lip much produced anteriorly, 

 as in Purpurina. This is the stage in which the shells are usually found. Larger 

 specimens have the aperture more circular. 



Relations and Distribution. — This may be regarded as the average form of 

 the goniata-grou]). It occurs throughout the Parkinsoni-zone, principally in 

 South Dorset, being especially abundant at Burton Bradstock, Loders, &c. It 

 also occurs in the upper part of the Humph ricsiaiivs-zone at Louse Hill, and in the 

 Parkinson /-zone at Grove, &c. Casts of this form are found in the Parhinsoni- 

 or Martinsii-zone of Midford. Purpurina Bella, d'Orb. (T. J, ii, pi. cccxxx, 

 figs. 9, 10), is perhaps nearly the same. 



