REPORT ON THE MONAXONIDA. 141 



definite, rounded or oval pore-areas (PI. XXX. fig. 2a) about 1 mru. in diameter; these 

 pore-areas are often very thickly scattered over the surfiice of the sponge, being separated 

 from one another only by thin strands of tissue. The dermal membrane within the 

 pore-areas is reduced to a fine, lace-like network by the presence of numerous large pores, 

 of which from thirty to forty often occur in a single pore-area. The pores themselves 

 are rounded openings, usually oval, but often more or less polygonal and varying in 

 greatest diameter from 0"07 to 0'35 mm. 



Skeleton. — (o) Dermal; a loose reticulation of scattered tylota, often arranged in 

 small brushes, in a radiate manner, around the pore-areas, (b) Main ; a very loose and 

 irregular reticulation of styli, united together in parts to form loose fibres ; rather 

 abundantly echinated by smaller, s^^ined styli. 



Spicules. — (a) Megasclera; of three kinds. (1) Styli (PI. XXVII. fig. 15), entii-ely 

 smooth or slightly spined at the base ; stout, usually slightly curved, and tapering 

 gradually to a very sharp point at the apex; size about 0"52 by 0'03 mm; making up 

 the main skeleton. (2) Much smaller, entirely spined styli (PL XXVII. fig. 15a), usually 

 straight, tapering gradually from the base to a sharp point at the apex; with the spination 

 more jironounced at the base than elsewhere, and often with distinct heads (tylostylote); 

 size about 0"18 by '01 3 mm. ; echinating the loose fibres of the main skeleton. (3) Tylota 

 (PI. XXVII. fig. 156), with straight, smooth shaft and slightly expanded heads, which are 

 very short and abruptly truncated, often slightly spined at the end; size about 0"33 by 

 0'0063 mm.; dermal, (b) Microsclera; tridentate isochelse (PL XXVII. figs. 15c, Ibd), 

 with strongly curved, stout shaft; variable in size, measuring up to about 0*044 mm. 

 in length; exceedingly abundant, especially in the dermal membrane. Occasionally 

 smooth, simple sigmata are seen, about 0"09 mm. long, but so rarely as to suggest that 

 ■ they probably occur only as foreign bodies. 



A remarkable feature of this species is the frequent truncation of the heads of the 

 tylota, often accompanied by minute spination. This, however, is not a constant feature 

 and may sometimes be observed in Myxilla rosacea, Schmidt; it may also occur in 

 Myxilla cribrigera, nobis. The two species, Myxilla cribrigera and Myxilla nobilis 

 agree closely in several respects, but are sharply distinguished from one another by the 

 fact that the former has no echinating spined styli such as are present in the latter. 



Another very interesting point is the transitional character of the larger stylote 

 spicule ; it is apparently normally smooth, but may be slightly spined {cf. Myxilla 

 paucispinata, nobis, p. 132). 



Localities. — Station 148a, January 3, 1874, lat. 46° 53' S., long. 51° 52' E.; south of 

 the Crozets; depth, 240 to 550 fathoms; bottom, hard ground, gravel, shells. One 

 specimen, apparently a piece broken off" from a larger one. Probably belonging to a 

 slight geographical variety. 



Station 320, February 14, 1876 ; lat. 37° 17' S., long. 63° 52' W.; off" the mouth of 



