ARCELLA VULGARIS. 139 



is compressed, its surface is parallel to the base and 

 almost half its width. The lateral margins form six 

 or eight obtusely-angular facets, the divisions of which 

 are faintly distinguishable in face view; the neck is 

 broadly inverted and extends upwards into the cavity 

 of the test to about one third the distance separating 

 the base from the crown. 



Dimensions : Diameter in face view averaging 100 

 to 120 /x; from base to crown in side view about 45 /x,. 



In Sphagnum from Dolgoch, Merionethshire, Aug., 

 1905. 



This variety is one of the numerous forms figured 

 by Leidy under the general name of Arcetta vulgaris, 

 but is so distinct, and so evidently a permanent form, 

 that its separation as a variety approaching A. angulosa 

 is desirable. Penard figures it (loc. cit.) as a European 

 form of A. artocrea, but this species, according to 

 Leidy, though pitted with surface-depressions, has an 

 arched crown. Gr. S. West also (' Journ. Linn. Soc.,' 

 Zool., vol. xxviii) figures it thus. 



Arcetta vulgaris var. compressa is rare. We have 

 only met with it in Merionethshire. 



FIG. 28. Arcella vulgaris var. compressa (face and lateral views, in 

 outline). In Sphagnum from Dolgoch, Merionethshire, x 260. 



