434 GASTEROPODA OF THE INFERIOR OOLITE. 



Bibliography, Sfc. — It should not be forgotten that the types of PI. actinomphala 

 occur in the " Maliere " of Normandy, a bed underlying the " Oolithe ferrugineuse." 

 Deslongcharaps speaks of it as being common in the condition of casts. It so 

 happens that in the Goncavus-bed at Bradford Abbas, which should be somewhat 

 about the horizon of the "Maliere," i.e. in the Lower Division of the Inferior 

 Oolite, a group of Pleurotomaria occurs, exhibiting great variety both as to size 

 and form, but which, without using varietal names, it may be convenient to focus 

 under PI. actinomphala. 



Similarly, it seems probable that considerable variety exists in the specimens 

 from France, if we are to regard the figures of Deslongchamps and d'Orbigny as 

 representing the same species. 



Description. — Amidst a multiplicity of fossils of all ages and sizes, aud with 

 much variety of character, there are two groups of varieties which attract our 

 attention. 



Acute Variety (PI. XXXVII, fig. 7, and PI. XXXVIII, fig. 5).— The form is 

 conical, and the shell may have a smooth periphery as in the first figure, or a 

 rugose periphery as in the second. Generally speaking, this form is rugose in 

 ornament, and it seems, on the whole, more nearly to represent the PI. actinomphala 

 of the French authors. It is also intimately related to PI. oxytera, described above, 

 though the whorls are always more tabulate. 



I have specimens of this variety, chiefly from the Concavus-bed at Bradford 

 Abbas and Halfway House, also from Dundry, and even from the neighbourhood 

 of Sherborne. 



Obtuse Variety (actinomphala-abbas) : 



Height (moderate size) . . .42 mm. 



Basal diameter . . . .65 mm. 



Spiral angle. .... 110°— 115°. 



Shell turbinate, depressed, largely umbilicate. Spire regular ; apex subacute. 

 Whorls (seven) subangular and inclined to be tabulate, increasing by steps ; in the 

 spire-whorls the suture is canaliculate. On the crest of each whorl is a corona of 

 tubercles, which are regular, and there is a certain amount of spiral ornamentation, 

 which is rather worn off in the older specimens ; there is no trace of a second carina 

 of belt at the base of the whorls. 



The sinus-band is median, wide, and flat, showing some spiral lines in the 

 younger and better preserved specimens, but usually smooth and strap-like in the 

 later ones. The body-whorl is relatively very large, convex, and biangular, the 

 anterior angle being nodular to smooth according to age and condition. The base 

 is convex and without much trace of spiral ornament, except in very young shells; 

 umbilicus wide, steep, and like a " staircase " in the earlier stage, with large ribs 

 radiating therefrom, though scarcely reaching the margin. In the old shells these 



