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. (Héb. and 
Desl., p. 18, pl. 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 Parkinsoni-zone 
of South Dorset (P,), being far from uncommon 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 Broadwinsor, showing more ornamenta- 
tion than usual in the subapical whorls. The species has 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 asa 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. SPINIGERA DIDACTYLA, sp. nov. Plate ITI, figs. 6 a,66,6c¢; 6d, e, f, g. 
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 
