86 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 
It has only been after long consideration, and an ample comparison of specimens of 
various dimensions, that I have seen fit to adopt the view taken by Professor Morris in his 
‘Catalogue,’ and separate this shell both from Pholadomya deltoidea and from Pholadomya 
Heraulti, of the Inferior Oolite. Compared with the latter form, it will be found that 
P. Phillipsii 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 rugee are more irregular and much less conspicuous, so that they only 
slightly indent the cost, these latter being less oblique than in P. Heraultt. The 
superior largeness and regularity of the rug, together with the deep indentations of the 
coste, is the feature which, at the first glance, impresses the spectator upon inspecting 
P, Heraulti ; the costee are usually somewhat more numerous, there being two anterior 
to the large coste 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 coste. 
Compared with P. de/toidea, Sow., the figure of the latter is more inflated, the costz 
larger and less indented, it also is without the angularity which is imparted by the second 
large costa of P. Phillipsii. 
Geological Position and Locality. Pholadomya Phillipsii is abundant in the Cornbrash 
of Scarborough, Gristhorpe, &c., and usually has the test preserved. ‘ 
PHoLADOMYA DELTOIDEA, Sow. Tab. XLII, figs. 4, 4 a. 
CARDITA DELTOIDEA, Sow. Min. Con., t. 197, fig. 4. 
PuHouapomya Murcuisoni, Sow. Ib., t. 545, the shorter figure only. 
_— BucARDIUM, 4g. Et. Crit. Myes., p. 77, pl. 5, figs. 3—7; pl. 5a, 
fig. 8. 
— — Chapuis and Dewalque. Fos. Ter. Sec. de Luxembourg, 
p. 124, pl. 18, fig. 1. 
— a Damon. Geol. Weymouth, p. 17, fig. 6. 
_ SOLITARIA, Mor. and Lyc. Gr. Ool. Moll., part 2, p. 124, tab. xii, fig. 2, 
et tab. 11, fig. 1. 
This species, so abundant in the Great Oolite, Fuller’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 costé 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. solifaria. Of these latter, the index facing Tab. XII, fig. 2, by a 
typographical error, was printed P. od/ita, 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 
