358 Pr.FISTOCENF. GKOI.OGV OF THE THAMES VALLEY. 



Unio littoralis, Lam. Not found by us. Examples in 



the Natural History Museum. 



Unio pictorum, Linn. Not found by us. Examples are 

 preserved in the Prestwich collection in the Natural History 



Museum. 



Unio tumidus, Retz. Abundant, but most of the speci- 

 mens were small, and owing to their condition it was only with 

 extreme difficulty that perfect examples were obtained. 



Anodonta cygnea, Linn. Numerous broken examples in 

 the clay. 



Corbicula fluminalis, Miill. Very common, but though 

 examples were obtained ranging from the fry to the adult none 

 of the specimens can compare in point of size with Crayford 

 examples. A pair of valves obtained from the base of the shell 

 bed still retained traces of their coloration. 



Sphaerium corneum, Linn. Common. Most of the 

 examples were intermediate between typical corneum and var. 

 mananmn. 



Pisidium amnicum. Abundant. Many of the examples 

 were very large and much inflated, a variation which is appar- 

 ently confined to Grays. Numerous specimens of the variety 

 daniihialis were found. This variety is well marked, resembling 

 in shape P. fontinale, but it is of course very much larger. This 

 variety was first found at Crayford, and on examples being sub- 

 mitted to Dr. O. Boettger, he identified them as var. danuhialis. 

 We liave not seen recent British examples, though it is living on 

 the Continent. 



Pisidium astartoides, Sandb. Very common. This is a 

 well marked species and though strongly sulcate specimens of 

 P. aiuiiicuin may somewhat approach it, yet its shape and the 

 sulcate umbo at once distinguish it. 



Pisidium pusillum, Gmel. Recorded by S. V. Wood. 



Pisidium fontinale, Drap. Very abundant. 



There is now a total of sixty-one species known or recorded 

 from Grays ; fort) -nine being from existing examples and 

 twehe on authority, a longer list, with the exception of Ilford, 

 than from any other Pleistocene deposit in the Thames Valley. 



