16 Messrs. G. S. Brady end D. Robertson on the 
to half the length: seen from the front, ovate, widest below 
the middle, pointed above, broadly rounded below. Shell 
thin, semitransparent, sparingly and minutely punctate, or 
often perfectly smooth, somewhat granular in appearance. 
Colour yellowish or reddish brown. Length s% inch. 
Hab. Dykes on the site of Whittlesea Mere, “ Whittlesea 
Dyke ;" rivers Nene at Peterborough, Cam at Ely, and Ouse 
at Lynn; Wroxham, Barton, Somerton, and Ormesby 
Broads. 
Though generally distributed throughout the East-Anglian 
district, this remarkable species appears to be rather rare as to 
number of individuals; nor have we succeeded in finding a 
trace of animal structure in any specimen that we have exa- 
mined. The minuteness of the shell may perhaps partly 
account for its apparent rarity; and as we have not met with 
it except in dredged material, we presume that it is a creeping 
rather than a swimming species, and probably inhabits ex- 
clusively the muddy bottoms of the broads and rivers. 
Genus ArcitLacta, G. O. Sars. 
Argillecia(?) aurea, nov. sp. (P1. VIII. figs. 4, 5.) 
Carapace, as seen from the side, compressed, subovate, some- 
what depressed in front, nearly of the same height through- 
out; height much less than one-half of the length; extre- 
mities rounded, the anterior narrowed and oblique: superior 
margin straight or very gently convex in the middle, curv- 
ing gently downwards at each extremity; inferior very 
slightly convex along its whole length. Seen from above, 
ovate, acuminate in front, rounded behind; greatest width 
situated in the middle, and about equal to the height. Sur- ' 
face of the shell quite smooth; colour golden yellow. 
Length 5}, inch. 
Hab. River Ouse at Lynn. 
But one specimen of this species was noticed ; and we place 
it provisionally only in the genus Argillecia. 
Genus CANDONA, Baird. 
Candona candida (Müller), var. tumida. (PI. IX. figs. 13-15.) 
Throughout the East-Anglian district occurs a form of this 
species differing from the typical C. candida chiefly in its ex- 
cessive shortness and tumidity. In the female the greatest 
height is equal to nearly two-thirds of the length, and the width 
to more than half of the length. Seen from above, the extremi- 
ties are very abruptly tapered, giving an almost elliptical 
contour. The male is much more compressed, but more tumid 
than in the ordinary form of the species. The lucid spots are 
