PLACOGISTA. 43 



denticulated aperture-scales ; the plasma and pseudo- 

 podia are very similar; it is not improbable that the 

 aperture is capable of distension. Of the four species 

 comprising the genus two are provided with spines 

 and two are glabrous. P. glabra Penard, a robust 

 sphagnum-inhabiting species, has not been recorded 

 from the British Isles, and P. lem Penard has been 

 recorded only from Loch Ness. In the United States 

 of America is found a form of P. spinosa the test of 

 which is sparsely covered with acicular spines. 



Synopsis of the British Spkoies. 



Test large, bearing lanceolate spines which are confined to 

 the niargin. (1) p spinosa. 



i'est smaller, sub-circular in broad view, bearing all over 

 its surface short acicular spines of varying length. 



(2) P. jurassica. 

 'J'est broadly ovoid, glabrous ; inhabiting deep lakes. 



(3) P. lens. 



1. Placocista spinosa (Carter) Leidy. 

 (Plate XL, figs. 1-6 ; and figs. 128-130 in text.) 



Euglypha spinosa 



Oaetee in Ann. Nat. Hist. (3) XV (1865), pp. 290, 293, pi. xii, f. 13. 

 Abchek in Qrt. Jrn. Micr. Sci. (n. s.) XII (1872), p. 88 ; op. cit. XVI 



(1876), p. 237 ; in Proc. Dublin Micr. Olub, II, 1 (1873), p. 108. 

 Leidy in Proc. Acad. Pliilad. 1874 (1875), p. 226 ; op. cit. 1878, p. 172. 

 Paeona in Boll. Soient. II (1880), pp. 47, 48. 



ScHEWJAKorr in Mem. Acad. St. Petersb. (7), XLI (1893), viii, p. 98. 

 Placocista spinosa 



Leidy Fresbw. Bhiz. N. Amer. (1879), pp. 221-224, 290, pi. xxxviii ; 



in Proc. Acad. Philad. 1879, p. 162 ; op. cit. 1880, p. 339. 

 Hitchcock Synops. Preshw. RMz. (1881), p. 38. 

 AvBEiNTZEEP in Arch. Protist. VIII (1906), p 114 ; in Trudui S.- 



Petei-b. Obsbcb. XXXVI, ii (1906), pp. 105, 107, 295-296, pi. i, if. 



8, 11 ; pi. ii, f. 38 ; pi. iv, f . 60. 

 ScHOUTEDEN in Ann. Biol, lacustre, I (1906), pp. 368, 369, f. 44. 

 Placocysta spinosa 



Blochmann Mikr. Thierw. Siisswass. (1886), p. 14; ed. 2 (1895), p. 18. 

 Penaed in Mem. Soc. Geneve, XXXI, 1, ll (1890), p. 183, pi. x, ft 10- 



24 ; Faune Rbiz. Leman (1902), p. 580, f . 17 (p. 572) ; in Rev. 



Suisse Zool. XIII (1905), p. 611 ; op. cit. XIV (1906), pp. 131-136, 



pi. iv, fE. 8-10 ; in Brit. Antarct. Exped. I (1911), pp. 221, 250. 

 Eyfeeth Einfacb. Lebensf., ed. 3 (1900), p. 267. 

 West in Jrn. Linn. Soc, Zool. XXVIII (1901), p 328 ; in Ann. 



Scott. Nat. Hist. 1905, p. 90. 



