96 GASTEROPODA OF THE INFERIOR OOLITE. 



from D'Orbigny's description), and where this is not so, it would seem to be the 

 result of wear. The spirals are often faint, except in the lower part of the body- 

 whorl, where they are more prominent ; but there is much variation in this respect. 

 On the whole, the spirals are fewer and stronger in the anterior than in the 

 posterior area of each whorl, and in well preserved specimens are seen to be 

 decussated with fine longitudinal striee. 



Aperture subquadrate, inclining to rhomboidal ; columella scarcely reflexed ; 

 anterior groove more marked in some specimens than in others. Umbilical slit 

 variable. 



Relations and Distributions. — The forms described below, viz. P. " fusiformis " 

 and P. carino-crenata, are probably nothing more than varieties of the somewhat 

 variable species identified as P. bianor. But this section of the genus Purpurina, 

 as was noticed by Hebertand Deslongchamps in dealing with P. granulata, recalls 

 the form of Amberleya (Eucyclus) with considerable force. It will be remembered 

 that many species of eucycloid Puvpurinm were figured by D'Orbigny in the ' Ter- 

 raines Jurassiques,' e.g. P. ornata, P. bathis, P. belia. Forms greatly resembling 

 these our palaeontologists have hitherto treated as belonging to the genus Amberleya. 

 It is difficult to say where the line should be drawn, since many of the shells referred 

 to Amberleya show considerable anterior grooving when well preserved. Alto- 

 gether, the section of Purpurina which contains P. bianor is anomalous, and full 

 of difficulty, as we shall perceive in the sequel. 



In this country P. bianor is essentially a fossil of the Parkinsoni-zone, being 

 fairly abundant in P l5 Burton Bradstock Cliff, and in the same horizon at Vitney 

 Cross, and Upper Loders. In North Dorset it occurs sparingly in the Parhinsoni- 

 beds at Halfway House and Bradford Abbas. 



15. Puepurina (Euctcloidea) : Species or Variety related to P. bianor. Plate II, 



figs. 6 a, b. 



This shell differs from the preceding in having a somewhat smaller spiral angle, 

 and in its more fusiform outline. The body- whorl presents a distinctly defined base, 

 and the anterior portion of the whorls of the spire has less of an inward slope ; 

 consequently the whorls are less angular. The keels are richly crenulate; the 

 spirals above the keel consist of a well-marked line near the suture, and two others 

 which are fainter ; the spirals below the keel are two in number and stronger ; all 

 are finely decussated by axial striae. 



Aperture imperfect, but probably like the preceding. 



It is not impossible that this form may be a poor representative of Turbo sub- 



