30 THE VOYAGE OF H.M.S. CHALLENGER. 



bodies of carbonate of lime, for whicli we propose tlie name " Calcastrella," are not parts 

 of the skeleton produced by the Eadiolarian, but foreign bodies picked up by its extra- 

 capsular sarcode (in the same way as the Coccoliths are picked up by Tlialassicolla 

 sanguinolenta = Myxobrachia .'). These Calcastrella occur also in the calymma of 

 some Discoidea and other Eadiolaria ; they are either unicellular calcareous Algae, or 

 foreign bodies of other origin. The Collodarium, however, described as Tlialassicolla 

 morum and Calcaromma calcarea, seems to be a simple Actissa, which has picked up 

 a number of Calcastrella. 



The Challenger collection has yielded a number of other true Thalasso- 

 sphserida, which partly agree with Thalassosphcera in the simple structure of the 

 unicellular body (resembling Actissa), and partly differ from it in the development of 

 alveoles, either within or without the central capsule (similar to HialassoJampe and 

 ThalassicoUa). The solid siliceous spicula, which occur in great numbers scattered in the 

 calymma, agree perfectly in form with the spicula of the colony -building Sphserozoida. 

 A characteristic difference between the social and the solitary B e 1 o i d e a seems to h& 

 determined by the cleavage of the nucleus, which takes place in the latter vei'y late, in 

 the former very early. Therefore in the large central capsule of the mature solitary 

 Thalassosphserida, we commonly find one large nucleus in the centre, and a number of 

 oil-globules around it in the endosarc, or disposed in one layer on the inside of the 

 capsule-membrane (PI. 2, figs. 2, 5) ; whereas in the much smaller associated capsules 

 of the Sphserozoida one large oil-globule is j^laced commonly in the centre, and a great 

 number of small nuclei scattered in the endoplasm (compare above, p. 24). 



Synopsis of tJie Genera of Tlialassosphcerida. 



. ,, , -,, -.,. -.r . ., (' Spicula simple, . . .7. Thcdassosuheera. 



A. Alveoles neither within nor without the ^ t- i > i 



central capsule. ) c. • i i i i 



^ ( bpicula branclieil, 



8. Til alassoj-an th in in. 



B. j!^umerous large alveoles witlim the central I o • i • i n -m ^ • 



, , ° . ,, , V > bpicula simple, . . .9. Fliusemaiium. 



capsule (not m the calymma). j r i > s 



^, ,T 1 1 1 -11 • i.T 1 { Spicula simple, . . .10. ThalassoiiUmda. 



C. Xsumerous large alveoles within the calymma J i i > ^ 



(not in the central capsule). ) o • i i, i j n r ^i ■ 



^ '■ ' [ bpicula branched, . .11. Lampuxanfiuam. 



Genus 7. Thalassosphcera ,^ Haeckel, 1862, Monogr. d. Radiol., p. 259. 



Defnitioii. — Thalassosphserida without alveoles, with simple, uubranched, needle- 

 shaped spicula in the calymma. 



The genus ThcdassospluBra was founded by me in 1862 for those solitary Collo- 

 daria in which the simple central capsule is surrounded by scattered solid spicule. 



1 r/iatosso.92i'"f''0 = Sea-spbere ; Sa.'ha.acit, uCpaipa.. 



