24 BRITISH FRESHWATER RH1ZOPODA. 



Var. curvata var. nov. (Plate XXI, figs 1 and 2.) 



Test pyriform, curved, with a short cylindrical neck, 

 and a blunt mamillary protuberance on the crown ; its 

 two sides (as seen in one aspect) unequally convex ; 

 the pronounced curvature of the test produced by the 

 outer surface from the crown downwards, for about 

 three-fourths of the total length, being broadly convex 

 whilst the opposite side is convex for only one half the 

 total length, or less, and then carried downwards, con- 

 cavely in outline, so as to form the narrow neck. (In 

 another aspect of the test that is, viewed with the 

 broader convex surface towards the eye the sides 

 appear straight and approach each other gradually 

 till they reach the abruptly-truncated mouth. In this 

 aspect, moreover, the crown has a tendency towards 

 the acuminate form, though the shell is not in the least 

 compressed, and the coronal protuberance is slightly 

 deflected from the longitudinal axis.) External surface 

 overlaid with muddy particles, and opaque ; con- 

 sequently the protoplasmic contents of the test are 

 invisible. Pseudopodia normal, few in number. 



Dimensions : Length 240 /A; breadth 110/x. 



In pond at Chipperfield, Herts, 1904 (A. Earland}. 



This variety seems to be peculiar to the Chipperfield 

 pond. A considerable number of individuals and some 

 empty tests were examined and all exhibited the same 

 remarkable curvature. 



The coarser Difflngias exist in this pond in great 

 abundance.* The quality of the water, the nature of 

 the soil, or some other cause unknown, appears to 

 favour their growth and development. The variety 

 under notice occurs in association with D. oblonga 

 Ehrenb., D. crassa sp. nov., D. urceolata Carter, 

 Lesqnereusia modesta Rhumbler, and other species. 



* [A small pond overgrown with rushes, on the south edge and near the 

 east end of Chipperfield Common.] 



