CENTROPYXIS ACULEATA. 137 



Less common than the type, but not infrequently 

 met with in swampy ground. Very abundant amongst 

 damp moss on limestone rocks, Ingleton ; also near 

 Bowness, Westmoreland (G. 8. West). 



This variety seems to be the Arcella ecornis of 

 Ehrenberg, properly removed by Leidy from that 

 genus to Centropyxis as a variety of C. aculeata. Ex- 

 cept for its usually smaller size it might be regarded 

 as typical C. aculeata deprived of its spines. From 

 Arcella it differs essentially in its test, which, as a 

 rule, is heavily encrusted with sand-grains ; whilst 

 from C. Isevigata Penard, it is at once distinguished 

 by the character of the orifice, which is plain and not 

 invaginated. 



2. Centropyxis Isevigata Penard. 



(Fig. 27.) 



Centropyxis Isevigata PENARD in Mem. Soc. Phys. Geneve, 

 XXXI, no. 2 (1890), p. 151, t. v. ff. 42-44, 49-55, and 

 Faune Eliiz. Leman (1902), p. 306, ff, and p. 666. 



Test in face view nearly circular, usually slightly 

 compressed on one side, composed of chitinous material, 

 and covered with irregular surface-scales and an ad- 

 mixture of fine sandy or muddy particles, causing 

 opacity ; the mouth obliquely invaginated, its outer 

 margin broadly rounded, the orifice (terminating the 

 inverted neck) excentric and generally invisible. In 

 side view the outline of the test is nearly hemispher- 

 ical, being broader at the posterior extremity. In 

 this aspect it has some resemblance helped by the 

 surface-markings to some forms of Difflu-gifi, arcula, 

 from which, however, the character of the mouth and 

 the inverted neck at once distinguish it. 



Dimensions : Diameter in face view about 100 p. 

 (120-135 /i, Penard). 



In Sphagnum; at Dunham and Chelford, Cheshire, 

 and near Abergynolwyn, North Wales. 



