386 Mr. J. F. Walker on a Phosphatic Deposit. 
pieces of the shelly limestone containing Cyrene, which in the 
Wealden occurs in layers varying from | to 6 inches in thickness. 
From a careful consideration of these facts, the conclusion 
seems unavoidable, that the fossils contained in this deposit con- 
sist of some coeval with its formation, and also of organic re- 
mains derived from the denudation of the Wealden and of the 
Kimmeridge and Oxford Clays. 
The following are descriptions of the new species referred to 
in this paper :— 
Sphera Sedgwickii, n.sp. Pl. XIII. figs. 1 & 2. 
Shell globose, nearly equilateral, slightly gibbous, concentrically 
striated, the striz finer and more distinct towards the ventral 
margin; ligament prominent ; lunule large, distinct, cordate. 
This shell is very plentiful, though it is rarely found perfect. 
The largest specimens hitherto obtained do not exceed the fol- 
lowing dimensions :—length 1°6 inch, breadth 1-5 inch, thick- 
ness 1°3 inch. 
In its general form this shell closely approaches S. corrugata, 
Sby. (= Corbis cordiformis, D’Orb.); the striation of the surface, 
however, is much finer, especially towards the margin; the 
lunule is very distinctly marked. The anterior margin is also 
destitute of the opening at the lower end of the lunule, repre- 
sented in D’Orbigny’s figure. I have obtained two specimens 
with the valves united, which show no traces of having been 
rolled. The other specimens are generally more or less frag- 
mentary. 
The fossil is named in honour of the venerable Professor who 
first discovered Sphera corrugata. 
Pholas Dallasii, nu. sp. Pl. XIII. figs. 3 & 4. 
Shell somewhat ovate, short, inflated, attenuated at the anal ex- 
tremity, transversely divided by a single, nearly horizontal, 
punctate furrow; the surface on each side of the furrow finely 
striated; the striz on the buccal side nearly parallel to the 
margin, those on the anal side less distinct, abbreviated, and 
obliquely directed towards the dorsal margin. 
This little Pholas, which occurs in small pieces of wood mine- 
ralized by phosphatic salts, is very nearly allied to P. Cornue- 
liana, D’Orb., from which, -however, it seems to differ abun- 
dantly in its shorter form, which is more attenuated towards the 
anal extremity, the more horizontal direction of its single punc- 
tate furrow, and apparently the greater prominence of its um- 
bones. 
I have great pleasure in naming this fossil after my friend 
W.S. Dallas, Esq., F.L.S. 
