106 GASTEROPODA OF THE INFERIOR OOLITE. 



Relations and Distribution. — Distinguished from Sp. longispina in being much 

 shorter, although with nearly the same number of whorls ; also in the marked bicari- 

 nation of the anterior whorls, and to a certain extent in the direction taken by the 

 spines, some of which have a tendency to curve upwards. It is also more 

 compressed and the whorls less tumid. Spinigera compressa, D'Orb. (Heb. and 

 Desk, p. 18, pi. vi, fig. 8), from the Callovian of Montreuil-Bellay, which species 

 is regarded by the authors as synonymous with Muricida fragilissima, Quenstedt 

 (' Der Jura,' tab. 65, fig. 30), is a small form rather nearer to Sp. longispina than 

 to this species. 



Spinigera recurva is essentially a fossil of the lower part of the ParJeinsoni-zone 

 of South Dorset (P^, being far from uu common in the cliffs of Burton Bradstock 

 and Bridport Harbour, likewise in the quarries of the interior, especially at Vitney 

 Cross. I have also a stunted variety from Broadwiusor, showing more ornamenta- 

 tion than usual in the subapical whorls. The species bas been recognised by 

 M. Deslongchamps in the Bajocian of Normandy as one hitherto unnamed. 

 Undoubtedly the differences which separate it from Sp. longispina are not very 

 great, and some might be disposed to regard it as a variety. At the same time 

 these differences are constant or nearly so, and are coincident with a change of 

 horizon. When we feel sure that such is the case it seems only reasonable to 

 " make a new species." 



25. Spinigeea didactyla, sp. nov. Plate III, figs. 6 a, 6 b, 6 c ; 6 d, e,f,y. 



Description. — This is a very variable shell, especially as to size and angular 

 measurements ; or, stated in other terms, several forms presenting considerable 

 differences of size and outline are grouped under one specific distinction. The 

 dimensions, therefore, must be given subsequently under the heading " varieties." 



Shell elongate to sub-elongate, fusiform, and greatly compressed. Apex very 

 blunt. The three apical whorls smooth and tumid; the whorls immediately 

 succeeding have a median costated keel ; the two costated whorls show a basal rim 

 above the suture. The rest of the shell, consisting usually of five whorls in the 

 longer varieties, and of four whorls in the shorter varieties, is nearly plain, or pro- 

 vided only with fine spiral lines. The keel is well developed, and ranges from 

 submedian to anterior in position. These whorls develop the bilateral varices, 

 which send out short spines on crossing the keel. The body-whorl is strongly 

 bicarinate, sending out from each keel two long channelled bifurcating spines, 

 which greatly resemble the double wing of the didactyl Alarias. 



The aperture is subquadrate or trapezoidal, with the outer lip distended over 



