spox<:iiii\. 171 



of that form, in its incrusting habit (purpurea being massive), in 

 the inferior diameter of the shaft of the spinulate and the superior 

 length of the spinispirular spicule (in purpurea these dimensions 

 are respectively '013 and -016 millim.), the latter usually consisting 

 in purpurea of only one to one and a half bends. 



The single spirit-specimen measures 32 millim. {\\ inch) in 

 height by 30 millim. in longest diameter, by L0 millim. (i inch) 

 in greatest thickness. 



TETRA CTIXELLIDA. 



The family Idthistidce is not represented. This is not surprising 

 if it is remembered that the depths investigated did not exceed 40 

 fms. Mr. Carter's better fortune with collections from Ceylon is in 

 part due to the greater depth at which the specimens were obtained. 



cho-pistole. 



Sottas, Ami. $ 3Iag. N. H. 1882, ix. p. 164. 



Prof. Sollas has since proposed a different arrangement of the 

 Tetractinellida, but the division into Choristidae and Lithistidas 

 appears a natural and convenient one. The species obtained, 

 though few in number, are of remarkable interest, and all new to 

 the Australian seas. 



STELLETTA, Schmidt. 



This genus, as at present constituted, is decidedly heterogeneous. 

 Some of Schmidt's and Carter's species appear referable either to 

 Geodia, or some genus intermediate between Geodia and Stelletta 

 (by virtue of the transitional character of their ball-stellate spicule), 

 while S. euastrum appears distinct by virtue of its disks. The more 

 typical forms appear to be divisible into subgroups which coincide 

 roughly with their geographical distribution. Thus the Atlantic 

 species mostly have medium-sized stellates, with numerous rather 

 coarse, pointed rays ; the Indo-Pacific ones have few-rayed stellates, 

 usually minute ; of the latter, the Fijian and two of the Ceylon 

 forms agree in having a small surface bacillate or acerate spicule, 

 while one Ceylon form (S. tethyopsis) and all the Australian ones 

 known at present agree in having only minute delicate rayed 

 stellates. 



The Indo-Pacific species of Stelletta, s. str., may be divided into 

 two groups : — 



Group 1. With bacillar or acerate flesh-spicule. 



1. S. (Ecionemia) acervus, Bowerbank, P. Z. S. 1873, p. 322, 

 pi. xxx. figs. 1-6. Fiji Islands. 



2. S. (Ecionemia) densa, id. I. c. p. 322, pi. xxx. figs. 7-14. Fiji 

 Islands. 



3. S.(Tisijjhonia) nana, Carter, Ann. & Mag. X. H. 1880 v. 

 p. 138, pi. vii. fig. 43. Gulf of Manaar, Ceylon. 



