pronounced. Its width exceeds its length; it has a small, 
hut wide, mesial fold, and the beak is very closely pressed 
down on the smaller valve. Dimensions are: length, 9, 
breadth, 10 J, depth, 6 lines. A more gibbous variety occurs 
at Broadwindsor, in which the mesial fold, though elevated, 
is very shallow; length, 11, breadth, 12, depth, 10 lines. 
Another variety is small, narrow without mesial fold, but 
very coarsely-ribbed; length, 7, breadth 7|, depth 5 lines. 
It occurs at Bradford Abbas. A broad variety possesses 
no actual fold, but an arching of the margin accompanying 
a slight convexity in the larger valve. Its dimensions are : 
length, 10}, breadth, 13J, depth, 7\ lines. Localities, Bradford 
Abbas, and Broadwindsor. 
Yar. obornensis, Buckman and Walker. 
This variety is found very high in the Parkinsoni-zone, 
namely, in the almost unfossiliferous, sandy limestone, just 
north of Oborne village ; and it seems peculiar to that locality. 
It is distinguished by its flatness and very few' spines ; but 
some specimens are remarkable because they show a broad area 
along the margin of both valves, which is destitute of spines 
and ribs, and exhibits only numerous fine transverse lines. 
The geographical distribution of Acanthothyris spinosa and its 
varieties is practically co-extensive with the occurrence of the 
upper part of the Inferior Oolite—the Bajocien proper—in 
Dorset, Somerset, and Gloucestershire. Besides the places 
already mentioned, we have found it at Burton Bradstock, and 
its neighbourhood; at Walditch, Yintney Cross, Chideock, and 
other places near Bridport; at Stoke Knap, Broadwindsor, 
Bradford Abbas, Halfway House, and the quarries round Sher¬ 
borne in Dorset; a.t Stoford, Milborne Wick, near Blackford, and 
in the neighbourhood of Castle Cary, at Midford, and at 
Dundry, in Somerset; while in Gloucestershire it occurs 
along the whole range of the Cotteswold Hills, wherever the 
Upper Trigonia Grit is exposed. 
In Y orkshire, in the blue sandy limestone, a little above the 
Whitwell Oolite (upper part of Inferior Oolite), at Crambeek, 
near Castle Howard, we find a small globose variety, with a 
