PURPURINA. 89 



entire shell. Whorls about six, very angular. Posterior area flat, and forming a 

 right angle with the sides, which are compressed and slightly undercut in the whorls 

 of the spire. In the finer varieties (such as the specimen 5 a, b) there are from 

 twenty-two to twenty-five longitudinal costas on each whorl, but these only extend 

 about half way down the body- whorl. These costce form a circlet of slight spinous 

 nodes on the keels, and are continuous over the flat area. The spiral ornamentation 

 is similar to that of P. elaborata, and is not traceable over the flat area. 



The aperture is ovate and relatively small; the pillar is short, and slightly 

 reflexed, producing a broad and extremely shallow trough. Umbilical slit faint. 



Specimens showing a bolder character of ornamentation are figs. 5 c, d, 5 e, /. 

 Some of these have seven whorls. In the proportions and general shape of the 

 whorls these do not differ materially from what has been already described ; the 

 ornamentation is simply coarser. In a large series every gradation may be seen. 



Relations and Distribution. — In the character of its ornamentation, and in the 

 rectangular outline of the whorls, there is considerable similarity between this 

 species and P. elaborata; but the spire is higher, the shell less tumid, and the 

 aperture somewhat more restricted. 



In England P. bellona is most abundant in the Parhinsoni-zone of Burton 

 Bradstock and that district, where some specimens occur with a higher spire than 

 any shown on the accompanying plate. It also occurs in the Gadomensis-bed at 

 Oborne. Specimens from the Upper Division in the Cotteswolds may, perhaps, 

 belong here, but their condition is seldom good enough for specific determination. 



5. Purpurina bellona, D'Orbigny, var. pagoda. Plate I, figs. 7 a, b, c. 



1858. Cf. Quenstedt, Der Jura, Turbo serratus, p. 485, T. 65, fig. 7. 



Description : 



Length of a well-grown shell . .25 mm. 



Ratio of width to length . . . 74 : 100. 



Length of body- whorl to entire shell . . 60 : 100. 



Spiral angle . . . .68°. 



The spiral angle is wider than in the more typical form. The posterior area of 

 the whorls slopes outwards towards the keel, and then curves upwards before 

 falling over, and the ornamentation on the keel is highly nodular. 



Distribution. — P : of Burton Bradstock Cliff (p. 31) contains this form. 

 Another variety with sloping whorls (see PI. I, fig. 9 <x, b) is from the Gadomensis- 

 bed at Oborne. This resembles the figure of a Dundry specimen given by Tawney 



12 



