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



form in question from Ascetta primordialis, H., Mr. Ridley states — 1, that the minimum 

 diameter of its largest spicule-rays exceeds 0*02 mm. ; and 2, that it possesses a. special 

 dermal set of triradiate spicules, considerably larger than those subjacent to them. 



Now I have numerous specimens from the Australian coast, all of which, presenting 

 the auloplegma-form and being provided with pseudostomata, differ from Clathrina 

 poterium, R., only in one important character, viz., the presence in the membrane of 

 the pseudostome of sagittal, occasionally irregular triradiate, spicules, of the size of the 

 smaller subdermal spicules, and just of the same form as the oscular triradiate spicules 

 in my Leuconia dura (PL VII. fig. 7). If my supposition be true, and if such triradiates 

 were wanting in the Australian specimens examined by Prof. Hseckel, and in the 

 American ones described by Mr. Ridley — all these specimens having always presented the 

 auloplegma-form — only for the reason that the delicate pseudostomial membrane 

 was torn off in the dredging, — the species Leiicosolenia poterium would receive still 

 sharper determination, both by its constancy in form (auloplegma) and by the presence 

 of peculiar triradiate spicules in the peristomial membrane. This latter character I 

 consider to be particularly important, for the triradiate spicules in question I find in all 

 the specimens I have of my conjectural Leucosolenia poterium, wdiile with respect to the 

 special dermal set of larger triradiate spicules, these specimens present a series of transition- 

 forms, beginning with those whose outer spicules are almost of the same size as those 

 of the interior of the colony, and ending with forms whose dermal triradiate spicules are, 

 each ray, 0"3 mm. long, and 0'035 mm. in diameter; in all these cases the rays of the sub- 

 dermal spicules, in accordance with Prof. Hseckel's statements, being 0'12 to 0"18 mm. long, 

 and - 006 to - 01 thick. Some subdermal spicules show an incipient fourth ray. 



I found in the specimens neither ova nor larvae, and the spermospores, sparsely 

 scattered here and there, were the only generative elements I observed in the examination 

 (PI. III. figs. 1 and 2). 



Colour. — White and yellowish. 



Habitat.— Station 163, AprU 4, 1874; lat., 36° 56' S., long., 150° 30' E. ; off Two- 

 fold Bay, Australia; depth, 120 fathoms,. 



Leucosolenia lamarckii, Hseckel, sp. 



Ascaltis lamarckii, Haeckel, Kalkschwamrne, Ed. ii. p. 60. 



The two specimens of this species were found attached side by side to an alga, both 

 presenting the auloplegma-form, and each being provided with a pseudostome. The 

 larger specimen has rounded angles, the smaller is an oval cylinder ; the longitudinal axis 

 of the larger attains a length of 9 mm., that of the smaller one does not exceed 5 mm. 

 The measurements of the spicules agree with those of Hseckel for his Ascaltis lamarckii, 

 var. agassizii; all the spicules, however — not only the larger triradiate — showing a 



