BIVALVIA. 57 



Spec. Char. " Testa elongatd, cuneiformi, trigond, angustd, sublavigatd, vel sulcis 

 longiludinalibus, superficialibus, unduJatis inslructd, ex/its fused, fibrosa, intus albd, 

 margaritaced." 



" 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 {Dixon), Highgate (Sowerbg). 

 France, Grignon, Parnes (Des/i). 



" This appears to have sharper ribs than P. affuiis, but probably they are the same 

 species differently preserved." (J. Sowerbg.) 



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. affnis. 



4. Pinna fyrifoumis, S. Wood. Tab. X, tig. 2, and Tab. XI, fig. 10. 



Pinna — n. s. Preslwich. Quart. Journ. Geol. Soc, vol. iii, p. 3/0, 1847. 



Spec. Char. P. testa tenui, tumidd, inflatd, infundibuliformi, costatd ; coslis numerosis, 

 subundidatis ; 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, ? 



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. affinis 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 the 

 rays are nearly obsolete ; what there are remaining appear to have been smaller and more 

 numerous, and also more equal, than those of affinis, 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. 



