142 
THE VOYAGE OF H.M.S. CHALLENGER. 
relied on for specific or even varietal distinctions. In some of the specimens from Station 
163a and from Port Jackson the dichotrisenes are characterised by cyathiform cladomes 
(PI. XIII. fig. 19) [i.e., the protocladi are curved as along the sides of a cup), in others 
the cladomes are infundibular {i.e., the protocladi are straight, diverging as along the 
sides of a funnel) (PI. XIII. fig. 3). The cyathiform character is found to vary consider- 
ably, so that sometimes the cladomes approximate to the infundibular type, and at others 
become more cyathiform than usual ; indeed, variations in this respect may be observed 
in the same individual sponge. 
Carter has made use of the angle which the cladi of the chief trisenes make with the 
rhabdome in the Geodiidse to separate the sponges of this family into smaller groups ; 
it is true that a character which is inconstant in one family may become of great 
importance in another, but it does not seem probable that a character which is not even 
of varietal importance in the Stellettidse can be employed for making large divisions in 
the Geodiidse ; nor, on further examining into the value of this character in the Geodiidse, 
do we find it more constant there than from the present instance we might expect. 
The limits assigned to the dimensions of the spicules in the description above given 
were obtained from an examination of a considerable number of specimens, and apply to 
the species, not to the individual ; within the limits of an individual the range of varia- 
tion is comparatively slight. I do not suppose that this species is markedly more 
variable than others I have described ; the simple explanation lies in the fact that more 
specimens were examined. 
The smallest specimen measures about 8 mm. in diameter, the largest 48 by 38 by 
40 mm. 
The ectosome, which on an average is about 0'08 to 0'09 mm. thick, consists of 
cavernous collenchyma, and is so extensively excavated by the ectosomal canals that 
the tissue is restricted to forming the roof and floor of these canals, and the connecting 
pillars which are traversed by the spicular sheaves. Transverse vela, perforated by 
sphinctrate apertures, cross the ectosomal canals at intervals. Fusiform cells are present 
in the collenchyma, especially in the roof of the ectosomal canals ; they are not more 
abundant in the floor, which passes into the choanosome, than elsewhere. Eound or 
oval cells containing somewhat large, round, deeply staining, highly refringent granules 
(PI. XIII. fig. 7) are common in the collenchyma, thickly dispersed through it; they also 
occur in the choanosome. The exterior of the ectosome contains a dense layer of 
anthasters. 
From the ectosomal canals others arise which descend radially, parallel to the spicule 
sheaves into the choanosome ; they are crossed at close intervals by the usual transverse 
vela. At the entrance of some of these canals into the ectosome, the latter is much 
thicker than elsewhere, and the ectosomal canal large and subdivided by horizontal parti- 
tions ; this appears to distinguish in some cases the excurrent from the incurrent canals. 
