D1FFLUGIA OVIFOEM1S. 53 



This pretty rhizopod is very uncommon. Its occur- 

 rence appears to be sporadic, and in the above-named 

 locality the only one we at present know of it 

 occurred in the summer of 1905 in extraordinary 

 abundance. Apart from the occasional five-lobed 

 mouth the test showed very little variation in the 

 scores of individuals examined. Every drop of water 

 squeezed from a tuft of Hi/pnum, which was found 

 growing on the half -submerged trunk of a tree, yielded 

 from two to half-a-dozen perfect examples. They 

 were preserved in a living and active state for many 

 months. 



This rhizopod differs from D. amphora Penard (' Les 

 Sarc. des grands Lacs,' 1905), in size, being consider- 

 ably smaller (110 (j. as compared with 200-210 /a), as 

 well as in the character of the crown and in the 

 general structure of the test. The organism is very 

 mobile. In size and general character it resembles a 

 form included by Leidy in D. lobostoma, and so figured 

 in ' Freshw. Rhiz. N. Amer.,' but the structure of 

 the mouth, no less than the surrounding collar, places 

 it beyond the limits of that species. 



A rhizopod with which D. oviformis might be con- 

 founded more readily than with D. lobostoma is Cucur- 

 liii'lld mespiliformis Penard, a species up to the present 

 time not known in Britain. It has a very similar wavy 

 collar round the mouth. The mouth however is a 

 circular orifice not lobed and it has a finely dentate 

 margin ; the test, moreover, is stouter in proportion 

 than that of D. oviformis, and the elements of which it 

 is composed have no resemblance to those of the species 

 under notice. 



22. Difflugia arcula Leidy. 

 (Plate XXII, figs. 8-11.) 



Difflugia arcula LEIDY (pars) Freshw. Rhiz. N. Amer. (1879), 

 p. 116, t. xvi, ff. 30, 31; in Pr. Acad. Philad. 1879, p. 

 163 : and op. cit. 1880, pp. 335, 338 ; HITCHCOCK Synops. 

 Freshw. Rhiz. (1881), p. 14; TAEANEK in Sitzber. bohni. 



