237 



iilA'i' 



o:n" the seasonal distribution of some 



QUEENSLAND SPECIES OF ARCELLA Ehrenbero-. 



By C. D. Gillies, M.Sc, Biology Department, University of 

 Queensland. 



(Co'inmiinirafed hi/ Dr. T. Ifarn^y JiJinslmi. ) 



(With foiu- Text-fio'ures). 



(1.) General 



The Rliizopodan genus Arcella Elirenberu-, is represented in 

 the fauna of freshwater pools of Queensland so far investigated, 

 l)y four well difterentiated forms, viz., A. viihfaris Ehr., A. dis- 

 coides^hv., A. mitr<Ua T^eidy, and A. artocrea Leidy. On account 

 of the present condition of Rliizopodan taxonomy, these terms 

 are to be interpreted in this paper as follows : — 



A. vulc/aris Ehr., small, hemispherical forms in which the test 

 may be either smooth or gibbose. 



A. discoides Ehr., flat, disk-like species, with the alveoli of tlie 

 test very small. 



A. mitrata Leidy, test normally polygonal; alveoli conspicuous; 

 pylome with a double invagination. 



A. artocrea Leidy: under this appellation is included a number 

 of large forms in which, typically, the basal portion of the test 

 is rim-like. This feature ranges from being well developed to 

 absent, but, in a series, there is no questioning the identity of 

 the latter variant in spite of the loss of the rim. The fundus of 

 the test is hemispherical, and the alveolar markings are con- 

 spicuous. These forms may be regarded as the Queensland 

 representatives of the species described l)y Leidy under this name. 



A. dentata Leidy, has not been observed, though it has been 

 searched for. This may be on account of its rare occurrence, for- 



