10-t "TERRA NOVA" EXPEDITION. 



THOLOSINA, Rhumbler. 



1-11. Tholosinn bulla (Brady). 



Placopsilina bulla, Brady. 1879, etc., RRC. 1881, p. 51 ; 1884, FC. p. 315, pi. x.xxv, figs. 16, 17. 

 Tholosina „ Cusliman, 1910, etc., PNP. 1910, p. 49, fig. 55. 



Stations 26, 28, 38, 45, 46, 50, 53, 54, 55 (+ K. I., D.). 



Attains its maximum development in the Antarctic area, where it is common, 

 and extremely variable, attached to Zoophytes. There is a wide range in size, 

 the finest .specimens being from Station 55. Other large individuals at Stations 

 38 and 45. At some of the Stations where the species is abundant there is an 

 enormous range in the shape of the individual specimens, from low sessile 

 growths to high-domed, sub-globular, globular attached, and even (at Station 26), 

 globular free. The latter individuals can only be determined by their association 

 with their congeners ; taken apart they would be indistinguishable from specimens 

 of Thurammina papillata, Brady. The Antarctic specimens are, as a rule, very 

 dark in colour, owing to the character of the sand-grains, of which the test is 

 composed. At Station 28, attached to stems of a Campanularian, the branching 

 outgrowths from which pass right through the test of the Rhizopod, which has 

 constructed a wall round them. 



CRITHIONINA, Goes. 



The genus Critliionina, instituted by Goi'S in 1894, cannot be regarded as 

 entirely satisfactory. It probably includes several forms which, though closely 

 related, have no definable connexion with one another. The origmal diagnosis 

 of the genus is probably responsible for the resultant uncertainty as to its sys- 

 tematic position. Goi's" definition was as follows : — " Labyrinthic, or cavernous, 

 or with an undivided central cavity, provided with a sub-cavernous wall, with 

 scanty or indistinct apertures." Of the species originally described, C. granum 

 may be regarded as the simplest type, and forms, in its many varieties, a Imk 

 connecting the other species assigned to the genus. C. granum in its external 

 form may, practically, be of any shape — typically it is a compressed sphere. 

 C. mmnilla is, practically, always sessile, an attached hemispherical body, from 

 the outer walls of which project spicules or shell-fragments, irregularly disposed. 

 In both species the walls are thick, and built up of fine sand-grains, held 

 together with a minimum of cement. In 1896 Goes added three other species to 

 his genus, C. pisum, C. rugosa, C. lens, and variety C. granum, var. sub-simplex- 

 C. pisum, which, in its most typical form, as commonly found in North Atlantic 

 oozes, is a small pea-shaped (pisiform) shell, of smooth exterior, and thick wall, 

 exhibiting, when laid open, but a small central cavity, but which tends, wherever the 

 species occurs in any quantity, to vary in a retrograde direction, towards C. 

 graniwi, and in a progressive direction towards C. rugosa, which may be regarded as 



