52 
well marked mesial fold of six or seven plaits. Unfortunately, 
most of the shells are very much crushed. 
Yar. powerstockensis, Buckman and Walker. 
A variety of Acanthothyris spinosa occurs at Eype, West 
Bay, Bridport, in the lower part of the Fullers Earth, and also 
in the same horizon in the railway-cutting near Powerstock 
Station, Dorset. These specimens are convex, with a wide ill- 
defined wave-like fold, forming a depression in the middle of 
the larger valve, and having fine numerous ribs well covered 
with spines. This shell is not uncommon, hut perfect specimens 
are rare. Acanthothyris spinosa occurs sparingly in the Fullers 
Earth rock of Whatley, near Erome, Somerset. We have not 
found any specimens of Acanthothyris in the Upper Fullers 
Earth. 
Acanthothyris paucispina, Buckman and Walker. 
1882 ? Rhynchonella Crossi, Haas (non Walker F), Brack. 
Juraf., Abk. z. geoh, Spez. 
Karte v. Elsass-Lotkingen, 
Bd. ii., PI. vi., Fig. 5. 
Generally broader than long ; the imperforate valve strongly 
convex, ornamented with coarse ribs, bearing a few coarse 
spines. The mesial fold of four or five coarse ribs, and some¬ 
times very much elevated. The beak is small and fairly pressed 
down on the other valve. 
Its generally greater width, and the depressed character of 
the beak, separate it from the form figured in the above 
reference, to which, however, it bears much resemblance. 
It is much larger than Acanthothyris Crossi , Walker, possesses 
more ribs and a less elevated mesial fold. About the same 
size as Acanthothyris spinosa , it differs therefrom by its coarser 
ribs, fewer spines and more pronounced, more elevated mesial 
fold. 
The Sauzci-IIuniphrcsianiwi- zone, of Dundry, yields most 
specimens of this species; it occurs at Oborne, in the Hum - 
phresianum- zone, but very rarely. In the Sauzei-zone of that 
locality it is generally very small, the mesial fold is scarcely 
developed, and the specimens are not characteristic. 
