86 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



It lias only been after long consideration, and an ample comparison of specimens of 

 varions dimensions, that 1 have seen fit to adopt the view taken by Professor Morris in his 

 ' Catalogue/ and separate this shell both from PUoladomija deltoidea and from Pholadomya 

 IlerauUii of the Inferior Oolite. Compared with the latter form, it will be found that 

 P. PJdllijjsii has the anterior side more truncated, and the posterior side gapes with a 

 larger aperture ; this latter feature is, in fact, distinguishable in shells of all dimensions ; 

 the longitudinal rugae are more irregular and much less conspicuous, so that they only 

 slightly indent the costse, these latter being less oblique than in P. Heraulti. The 

 superior largeness and regularity of the rugcE, together with the deep indentations of the 

 costse, is the feature which, at the first glance, impresses the spectator upon inspecting 

 P. HerauUi ; the costse are usually somewhat more numerous, there being two anterior 

 to the large costse and an additional one posterior to it, so that, together with their 

 greater obliquity, only a small portion of the posterior side of the shell is destitute 

 of costae. 



Compared with P. deltoidea. Sow., the figure of the latter is more inflated, the costse 

 larger and less indented, it also is without the angularity which is imparted by the second 

 large costa of P. Pliillipsii. 



Geological Position and Locality. Pholadowya Phillijmi is abundant in the Cornbrash 

 of Scarborough, Gristhorpe, &c., and usually has the test preserved. 



Pholadomya deltoidea. Sow. Tab. XLII, figs. 4, 4 a. 



Caruita deltoidea, Siow. Min. Con., t. 197, fig. 4. 



Pholadomya Mukchisoni, 8oio. lb., t. 545, the shorter figure only, 



— bucardium, Ag. lit. Crit. Myes., p. 11 y pi. 5, figs. 3 — 7 ; pi. 5 a, 



fig. 8. 



— — Chapuis and Dewalque. Fos. Ter. Sec. de Luxembourg, 



p. 124, pi. 18, fig. 1. 



— — Damon. Geol. Weymouth, p. 17, fig. 6. 



— solitaria, Ilor. and Lye. Gr. Ool. Moll., part 2, p. 124, tab. xii, fig. 2, 



ettab. 11, fig. 1. 



This species, so abundant in the Great Oolite, Puller's Earth, and Cornbrash of the 

 south of England, varies greatly in its general figure, even in the same bed and locality ; 

 and as its synonyms may now be considered as clearly ascertained, I have deemed it 

 desirable to figure a specimen from the Cornbrash of Wiltshire, in which the costse are 

 irregularly arranged, and the general figure is more lengthened than in the two specimens 

 formerly figured in the second part of the 'Monograph of the Great Oolite Mollusca,' 

 under the name of P. solitaria. Of these latter, the index facing Tab. XII, fig. 2, by a 

 typographical error, was printed P. ohlita, a shell which is given at fig. 5 upon the same 

 plate. Even the two Great Oolite specimens have the anterior side less truncated, the 



