138 BRITISH FRESHWATER RHIZOPODA. 



The test of C. Isevigata is not infrequently met with 

 in Sphagnum from the localities indicated, but from 

 its general opacity and resemblance to full-sized in- 

 dividuals of Difflugia arcula, is liable to be passed by. 

 The rounded margins of the oral orifice, and the 

 obliquely inverted neck, are sufficiently characteristic 

 features. 



FIG. 27. Centropyxis laerigata (face and lateral views). In Sphagnum 

 from Dolgoch, Merionethshire. x 260. 



Penard describes two other species of Centropyxis, 

 C. delicatula and C. arcelloides, both smaller than 

 that under notice, and having more or less external 

 'resemblance to Arcella vulgaris. They differ from (7. 

 Isevigata in the structure of the mouth and other 

 features. 



Genus ARCELLA (see pp. 118-121). 



Arcella vulgaris var. compressa var. nov. (Fig. 28.) 



Arcella vulgaris (pars) LEiDYFreshw. Rhiz. N. Amer. (1879), 



pi. xxviii, ft. 6, 7. 

 Arcella artocrea PENAKD Faune Rhiz. Leman (1902), p. 405, 



ff, (Non A. artocrea Leidy, 1879.) 



Test composed of thin chitinous membrane, yellowish 

 brown and semi-transparent, becoming darker with 

 age, and faintly punctated. In face view discoid, 

 irregularly oval, or sub-quadrate with rounded angles, 

 never truly circular; with a centrally-situated, com- 

 paratively small oval mouth. In side view the crown 



