386 Mr. J. F. Walker on a Phosphatic Deposit. 



pieces of the shelly limestone containing Cyrena, which in the 

 Wealden occurs in layers varying from 1 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 : — 



Sphara Sedgwichii, n. sp. PI. XIII. figs. 1 & 2. 



Shell globose, nearly equilateral, slightly gibbous, concentrically 

 striated, the striae 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. corrugattty 

 Sby. {=:Corbis cordiformis, D'Orh.) ; the striatiou 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 Sphcej-a corrugata. 



Pholas Dallasii, n. sp. PI. 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 strise 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 difi*er abun- 

 dantly in its shorter form, which is more attenuated towards the 

 anal extremity, the more horizontal direction of it.- 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. 



