Dh 5 pu 
pel ~ BIVALVIA. 57 
4 Mi 
Ue 
Spec. Char. “ Testd elongata, cuneiformi, trigond, angustd, sublevigata, vel sulcis 
longitudinalibus, superficialibus, undulatis instructd, extus fuscd, fibrosd, iatus albd, 
margaritacea.” 
‘Shell elongate, wedge-shaped, trigonal, nearly smooth, or with superficial and longi- 
tudinally undulating rays, externally brownish or dusky and fibrous, within white and 
nacreous.” 
Length, ? 
Localities. —Bracklesham (Dizon), Highgate (Sowerby). 
France, Grignon, Parnes (Desh). 
“This appears to have sharper ribs than P. afinis, but probably they are the same 
species differently preserved.” (J. Sowerdy.) 
Our figure is taken from a specimen in the British Museum in the late Mr. Dixon’s 
collection ; this species appears to have more numerous and finer rays than any I have seen 
upon the young state of P. afinis. 
4. Pinna pyrirormis, S. Wood. ‘Tab. X, fig. 2, and Tab. XI, fig. 10. 
Pinna — nis. Prestwich. Quart. Journ. Geol. Soc., vol. ii, p. 370, 1847. 
Spec. Char. P. testa tenui, tumidd, inflata, infundibuliformi, costatd ; costis numerosis, 
subundulatis ; margine dorsali subrectd ; margine ventrali incurvd. 
Shell thin, tumid, or inflated, funnel-shaped, costated ; ribs numerous, thin, and slightly 
undulating ; dorsal margin nearly straight, ventral margin curved. 
Length, ig 
Locality. Cuffell, near Basingstoke (Prestwich). 
The specimen figured is from the cabinet of Mr. Prestwich, and I coincide in his 
opinion that it is specifically distinct; it is unlike any other species that I have seen. 
It differs from P. afinis in form, and it approaches nearer to P. arcuata; but it is not 
so curved as that species, either in the dorsal or ventral margin, and it is considerably more 
expanded than either of those species. A small portion only of the shell is left, and tlie 
rays are nearly obsolete; what there are remaining appear to have been smaller and more 
numerous, and alse more equal, than those of affazs, but its presumed distinction is founded 
upon the expanded character. I cannot but imagine this to be natural, for although there 
is a tendency in many species of this genus to become inflated by a collapse or fracture 
in the centre, I do not see in this any angularity, but a regular curvature in the valves. 
lo 4) 
