EEPOET ON THE TETRACTINELLIDA. 
201 
Spicules. — I. Megascleres. 1. Oxea, fusiform or cylindrical, sometimes tornote, 
1‘136 by 0’014 mm. 
2. Orthotrigene, rhabdome oxeate or strongylate, cladi of variable and unequal length, 
usually strongylate, straight or reflexed. Ehabdome 075 mm. and over in length by 
0‘0135 mm., cladi from 0‘009 to 0'045 mm. long. 
II. Microscleres. 3. Chiaster, centrum small or absent, actines slender cylindrical, 
terminally truncate or minutely tylote, 0’0125 mm. in diameter. 
4. Microstrongyle, cylindrical, entirely spined, spines small, conical, erect, 0'04 by 
0'0042 mm. This spicule is traversed by a distinct axial canal. 
Colour. — YeUowish-brown in the dried state. Size, 33 mm. high by 37 mm. in 
diameter. 
Habitat. — Port Adelaide, Australia, 
Remarks. — The ectosome is thin, about 0*5 mm. in thickness. The oxeas are 
partly aggregated into distinct fibres, which radiate to the surface, partly loosely 
scattered through the sponge. In the ectosome they lie tangentially. The trisenes occur 
along with the oxeas of the fibres, lying parallel with them ; from their comparative 
rarity and the variability and shortness of their cladi they appear to be undergoing a 
process of crowding out. The cladi are sometimes all three reduced to a length less than 
the diameter of the rhabdome, sometimes a cladus may attain a length of 0’045 mm., 
and the remaining two only half this, 0’023 mm.; sometimes one cladus may be absent 
altogether, only two remaining. When first I met with one of these spicules I imagined 
that it might be of extraneous origin, since the sponge has a habit of embedding foreign 
bodies, such as sand grains, in the ectosome ; subsequent examination proved that this 
could not be the case ; the triaenes are too numerous, too fresh, and too exactly similar in 
position to the trisenes which occur in undoubted triaenose sponges for such an explanation 
to be tenable. 
The discovery of triaenes in a sponge where they had escaped the lynx-eyed acuteness 
of Carter, who founded a new genus on their supposed absence, may well impress us with 
the untrustworthy nature of negative evidence, and has led me to examine and re- 
examine afresh such sponges as Asteropus, in which I have myself stated their absence, 
and although I have not succeeded in finding them, it by no means follows that no one 
else will. 
Although the definition given by Carter of the genus Stellettinopsis breaks down in 
its application to the typical species, yet there are other sponges to which it still applies 
good ; and the question arises whether we are to retain the name of the genus in con- 
nection with the definition or in connection with the typical species. It would obviously 
be more convenient to adopt the former alternative ; but there is a third course open, 
and that is to suppress the name altogether ; indeed, from this I see no escape. The 
(zooL, CHALL. EXP. — PART LXiii. — 1887.) Err 26 
