REPORT ON THE MONAXONIDA, 145 



fig. 10), more spined at the base than elsewhere ; slightly curved and tapering gradually 

 to a sharp point at the apex; size about 0'6 by 0'03 mm., forming the main skeleton. 

 It will be seen from their arrangement that all the spicules of the main skeleton are, in 

 a sense, echinating, so that we cannot distinguish between an echinating and a non- 

 echinating stylus as in some other Myxillm. There are, however, a great many stylote 

 spicules (PI. XXVII. figs. 10a, 106) which are much smaller (measuring about 0"28 by 

 0'013 mm.), and rather more strongly spined than those just described, but otherwise 

 very like them in form, and these are perhaps to be regarded as representing the true 

 echinating spicules ; it may be urged that they are merely young forms of the larger ones, 

 but their abundance and tolerable uniformity in size are against this view. (2) Tylota (PI. 

 XXVII. figs. 10c, lOcZ), usually slightly curved, rather stout, larger at one end than at 

 the other, with oval heads (sometimes not distinguishable), and spined at both ends, size 

 about 0'25 by O'Ol mm. ; dermal, {h) Microsdera; of two kinds — (1) very numerous 

 tridentate isochelae (PL XXVII. fig. lOe 10/), of peculiar form, the most noticeable 

 feature in which is the presence of a slight swelling in the centre of the curved shaft ; 

 length about 0'027 mm. ; (2) sigmata, usually much contort, size about 0"044 by 

 0-004 mm. 



The definite form, erect growth and elastic consistency of this sponge call to mind 

 the genus Clathria, and the arrangement of the skeleton recalls PlumohalicJiondria 

 rather than Myxilla, but the spiculation agrees very well with that of the genus to 

 which we have referred it ; in its genus it is further remarkable for the peculiar shape 

 of its isochelate spicule. 



ZocaZ%.— Station 170, 14 July, 1874 ; lat. 29° 55' S., long. 178° 14' W. ; off 

 Kermadec Islands; depth, 520 fathoms; bottom, volcanic mud; bottom temperature, 

 43°. One specimen. 



Myxilla (f) plumosa, Montagu, sp., vav. /usifera, nov. 



1818. Spongia plumom, Montagu, Mem. Wem. Soc. Edin., val. ii. p. 116. 

 1842. Halichondria (?) plumosa, Johnston, British Sponges, p. 103 

 1866. Mkrociona carnosa, Bowerbank, Mon. Brit. Spong., vol ii. p. 133. 



1866. Hymeniaeidon 2}lumosa, Boworbank, Mon. Brit. Spong., vol iL p. 195. 



1867. Pronax plumosa, Gray, Proc. Zool. Soc. Lend., p. 536. 

 1870. Desmai-idon plumosa, Schmidt, Spong. Atlant. Gebiet., p. 76. 



1874. Microeiona plumosa, Bowerbank, Mon. Brit. Spong., vol. iii. p. 61, pi xxiv. figs. 7-13. 



1880. Myxilla plumosa, Vosmaer, Notes from the Leyden Museum, vol ii. p. 126. 



1885. Plumohalieliondria plumosa. Carter, Ann. and jMag. Nat. Hist., ser. 5, vol xvi. p. 355. 



Sponge irregularly lobate. The largest specimen consists of an elongated base, from 

 which arise two lobes ; length of base not quite 25 mm., height of larger lobe 25 mm., 

 diameter about 8 mm. Coloior in spirit pale, greyish yellow. Texture soft, spongy, 

 elastic, rather tough and fibrous. Surface rather glabrous, but very uneven. Dermal 



(zool. chall. EXP. — PART Lix. — 1887.) Nnn 19 



