EEPORT ON THE MONAXONIDA. 143 



transparent. Oscula few, scattered, rather small. Pores arranged in definite, but 

 rather irregular groups (pore-areas), each group containing about twenty or thirty, 

 fairly closely placed, rounded or oval pores ; diameter of pores about 0"! mm. 



Skeleton. — Very irregular ; in parts one can distinguish primary lines of loose fibre 

 running vertically to the surface of the sponge, crossed by still looser secondary fibres or 

 by scattered spicules ; in other parts the arrangement is even less regular and may be 

 described as irregularly Halichondrioid. The fibre, such as it is, is composed of basaUy 

 spined styli, and is echinated by much smaller, entirely spined styli (also in places by the 

 larger styli ?). At the surface the main skeleton passes into loose fibres and brushes of 

 tylota. The latter are abundantly present in the dermal membrane, excepting in the 

 pore-areas, which are almost or quite free from spicules and have the tylota around 

 them arranged in a radiate manner. 



Spicules. — (a) Megasclera; of three kinds. (1) Basally spined styli (PI. XXVII. 

 fig. 14), sharply pointed and usually curved; size about '46 by 0-019 mm.; making 

 up the main skeleton. (2) Much smaller, entirely spined styli (PL XXVII. fig. 14a), 

 usually straight, sharply and very gradually pointed at the apex, sometimes with distinct 

 heads (tylostylote) ; size about 0'175 by 0'0125 mm.; echinating the skeleton fibre. (3) 

 Tylota (PI. XXVII. fig. 1 46), with straight shafts and very slight heads, which terminate 

 very shortly and abruptly and are flattened and slightly spined at the ends ; size about 

 0'3 by 0'006 mm.; dermal. (6) Microsclera; of one kind only, viz., tridentate isochelse, 

 with very strongly curved shafts ; size variable, up to about 0'034 mm. long. 



The most characteristic feature of this variety is the extent to which the flattening 

 of the ends of the tylota is carried ; the proj)ortions of the large spined stylus also 

 difier considerably from those of the corresponding spicule in the type specimens, as 

 will be seen by reference to the descriptions. 



XocaZ%.— Station 307, January 4, 1876 ; lat. 49° 24' 30" S., long. 74° 23' 30" W.; 

 ofi" the south-west coast of Patagonia; depth, 140 fathoms; bottom, blue -mud. Two 

 specimens. 



The species which we have called Myxilla nohilis, and its varieties, have given us a 

 great deal of trouble in determining their true relations ; they appear to be sufliciently 

 connected inter se to wairant us in considering them all as varieties of one species, and 

 that species perhaps finds its nearest already known ally in Bowerbank's Hymeniacidon 

 {^Myxilla) 2^aupertas ; the two species seem, however, to be distinct. Bowerbank apj^ears 

 to have had only very small and badly preserved specimens, about which nothing is 

 satisfactorily known excepting the spiculation, which, as evidenced by one of his 

 preparations in the British Museum, is as follows: — (l) Basally spined styli, verging 

 upon tylostylote, curved, attenuated and drawn out very gradually into very fine points ; 

 size up to about 0"52 by 0'012 mm. (2) Entirely spined styli (" internal defensive 



