48 BRITISH FRESHWATER RHIZOPODA. 



MURRAY in Proc. Roy. Soc. Edinb. XXV (1905), p. 615 ; in Bathym 



Surv. Scott. Lochs, I (1913), p. 326. 

 Placocista spinosa 



AVERINTZEFF (pars) in Trudui S.-Peterb. Obshch. XXXVI, n (1906), 



pp: 295-296. 

 SCHOUTEDEN (pars) in Ann. Biol. lacustre, I (1906), pp. 368-369. 



Test small, transparent, hyaline, glabrous, sub-cir- 

 cular in broad view, compressed, especially anteriorly ; 

 transversely lenticular ; aperture linear with undulate, 

 compressed lips, and a delicate membraneous border ; 

 plasma bluish-grey, granular, partially filling the test; 

 nucleus large, granular, containing from two to five 

 nucleoles ; one or more contractile vesicles usually 

 present ; pseudopodia filose, simple, radiating. 



Length 65-80 ^ ; breadth about nine tenths of the 

 length ; aperture about half the breadth ; thickness 

 about three sevenths of the breadth. 



Habitat. Deep lakes. 



SCOTLAND. Loch Ness, Inverness-shire (Penanty. 



Possessing a particularly fragile test, this species has 

 been recorded exclusively from the depths or shores 

 of large lakes. The only species with which it can be 

 confounded is P. glabra Penard, but that is found only 

 in sphagnum, it is larger, 90-1 05 /a in length, has an 

 aperture equal to about two thirds the breadth, and its 

 test is more robust and less transparent. It has not 

 been recorded from the British Isles. 



Dr. Penard, when kindly sending the writer a mounted 

 specimen of this species, pointed out a feature which 

 had previously escaped observation, namely, the pre- 

 sence beyond the aperture of a very delicate, hyaline 

 membrane with faint dot-like markings. The presence 

 of an exterior lip brings this species into close relation- 

 ship with the members of the genus Sphenoderia, but 

 considering the general shape, construction, and 

 appearance of the test it seems better, for the 

 present at any rate, to leave it in the genus Placocista, 

 where it may perhaps be regarded as a transitionary 

 species. 



