44 PLIOCENE MOLLUSCA. 



ribs, narrower than the intervening spaces, with exceedingly fine strife between 

 them ; umbo wide, depressed, subcentral ; ligamental fossnlge short, fairly deep ; 

 teeth, both cardinal and lateral, strong and prominent, differing somewhat from 

 those of P. amnicum.^ 



Dimensions. — L. 7 mm. B. 9 mm. 



Distribution. — Not known living. 



Fossil : Icenian Crag : Bramerton, Thorpe, Bulchamp. Fresh- 

 water bed : Corton, Kessingland, West Runton (not rare). English Pleistocene: 

 Erith, Clapton, Hackney, Clacton, Grrays, Crayford, Ilford and Swanscombe. 

 Pleistocene : Denmark. 



Bemarhs. — The charming little shell here figured, from a specimen in the Reeve 

 collection at the Norwich Castle Museum, is from the Icenian Crag of Bramerton; 

 it seems to have been known to S. V. Wood from Grays as a short, striated variety 

 of P. amnic'um, and to Dr. S. P. Woodward from Thorpe and Bulchamp under 

 Sowerby's name of P. aiiinicuiu, var. sulcata ; Mr. A. Bell informs me he found a 

 specimen of it himself at Bramerton. 



It is regarded by Prof. Sandberger, Messrs. Kennard and B. B. Woodward, 

 and by Mr. C. Reid as a species distinct from the Recent form P. amnicnin. It is 

 not rare at West Runton, where it is found in company with that shell and some 

 other species of the same genus. It is smaller, however, and less inequilateral, 

 with a rounder outline, the concentric ribs are fewer in number and more dis- 

 tinctly marked, especially at the umbones. 



Prof. Sandberger remarks that P. astartoides seems to correspond both in form 

 and sculpture with Bronn's description of P. co?iceui'r/c!(7?i from the Upper Pliocene 

 of Italy, but that as he had no specimens of the latter he had not been able to 

 compare the two. 



Pisidium casertanum (Poli). Plate I, fig. 19. 



1791. Cardium casertanum, Poli, Test. Utr. Sic, vol. i, p. 65, pi. xvi, fig. 1. 



1868. Pisidium casertanum, Lalleineut, Ann. Soc. Mai. Belg., vol. iii (Memoires), p. 59. 



1890. Pisidium casertanum, C. Keicl, Plioc. Dep. Brit., p. 230. 



1899. Pisidium pusillum (G-mel.), Kennard and B. B. Woodward, Proc. Malac. Soc, vol. iii, p. 202. 



1912. Pisidium casertanum, Kennard and B. B. Woodward, Quart. Journ. Greol. Soc, vol. Ixviii, 

 p. 234. 



1913. Pisidium casertanum, B. B. Woodward, Cat. Brit. Sp. Pisidium, p. 31, pi. i, figs. 3—6; 

 pi. iii, fig. 3 ; pis. xiii— xviii. 



Specific Characters. — Shell minute, fragile, rounded, ovate, rather convex ; 

 ornamented by excessively fine, irregular and inconspicuous concentric striae 

 (B.B. W.). 



1 The diiference is well shown h\ Mr. B. B. Woodward in an enlarged diawing of the hinge 

 (o/j. cit.), pi. ii, fig. 2. 



