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Order II. CONCHULINA. 



Family 1. AKOELLIDA. 



A. ARC ELLIN M. 



1. Arcella vulgaris var. hemisphaerica (Perty) 

 var. nov. 



(Plate LIX, fig. 5, and fig. 161 in text.) 



Arcella hemispherica 



PERTY Kenntn. kleinst. Lebensf. (1852), p. 186, pi. ix, . 5. 



PENARD in Mem. Soc. Geneve, XXXI, 2 (1890). p. 153, pi. v. ff. 93- 

 95 ; in Rev. Suisse Zool. IX (1901), p. 237 ; Faune Rhiz. Leman 

 (1902), p. 400, 4 figs. ; in Proc. R. Soc. Edinb. XXV, 8 (1905), 

 pp. 593, 596 ; Sarcodines in Cat. Invert. Suisse (1905), pp. 78-79. 



GODET in Bull. Soc. Neuchatel. XXVIII (1899), p. 78. 



WAILES & PENARD in Proc. R. Irish Acad. XXXI, LXV (1911), p. 65. 



WAILES in Jrn. Linn. Soc. Zool. XXXII (1912), pp. 123, 130. 



Test smaller than in the type, nearly hemispherical 

 in side view, the basal diaphragm forming nearly a 

 right angle with the circular dome as seen in vertical 

 section ; the base concave with a central circular 



FIG. 161. Arcella vulgaris var. hemispherica. Side view. x 250. 

 (After Cash.) 



orifice usually everted; plasma, nuclei, and 'con tractile 

 vesicles as in the type. 



Diameter of test usually 40 /A to 50 ft, sometimes 

 less. 



Habitat. Ponds and ditches. Generally distributed. 



Described by Perty under a specific name, this 

 variety is included in Vol. I, p. 120, by Cash among 

 the synonyms of A. vulgaris, but it seems to deserve 

 at least varietal rank. 



