PLACOCISTA. 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. lens 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 BKITISH SPECIES. 



Test large, bearing lanceolate spines which are confined to 

 the margin. (1) P. Sf>iw>sa. 



Test smaller, sub-circular in broad view, bearing all over 

 its surface short acicular spines of varying length. 



(2) P. jurassica. 

 Test 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 



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

 ARCHER in Qrt, Jm. Micr. Sci. (N. s.) XII (1872), p. 88 ; op. cit. XVI 



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

 LEIDY in Proc. Acad. Philad. 1874 (1875), p. 226 ; op, cit. X878, p. 172. 

 PARONA in Boll. Scient. II (1880), pp. 47, 48. 



SCHEWJAKOFF in Mem. Acad. St. Petevsb. (7), XLI (1893), vni, p. 98. 

 Placocista spinosa 



LEIDY Fresliw. Rhiz. N. Ainer. (1879), pp. 221-224, 290, pi. xxxviii ; 



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

 HITCHCOCK Synops. Freshw. Rhiz. (1881), p. 38. 

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



Peterb. Obshch. XXXVI, n (1906), pp. 105, 107, 295-296, pi. i, ff. 



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. 

 PENARD in Mem. Soc. Geneve, XXXI, 1, 11 (1890), p. 183, pi. x, ff. 10- 



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



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



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

 EYFERTH Einfach. Lebensf., ed. 3 (1900), p. 267. 

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



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



