STELOSPONGIA. 167 



consist of longitudinal main fibres, which are 0'l-0"28 millim. thick, and cored 

 with a pretty slender axial string of foreign spicule-fragments. They are 

 joined by short and simple transverse fibres 0-04-0-12 millim. thick, which are 

 free from foreign bodies. The meshes in the fascicles are square, round, irre- 

 gular, 0*2-0-6 millim. wide ; or oval, 0-4-0-6 milKm. long and 0*08-0-12 

 millim. broad. Such oval meshes are observed in S. a. canaliculata, S. a. conu- 

 lata, and S. a. viUosa. The interstices between these fascicles are occupied by 

 a pretty loose network of fibres, 0-04- O'l millim. thick, which are free from 

 foreign bodies. The meshes formed by them are 0"6-l'5 millim. wide, irre- 

 gular, or more often polygonal, with rounded corners. 



The inhalant pores are oval, 0-04-0-06 milhm. wide, and situated in small 

 groups on the outer surface of the sponge. There are no inhalant pores at all 

 in the walls of the wide central cavities, which are true oscular tubes. jN^o 

 small circumvallate oscula are situated on the surface. The inhalants lead into 

 slender canals, which open into tangeutially extending canals 1-1*5 millim. 

 wide, from the floors of which large inhalant canal-stems originate, which are 

 straight, cylindrical, and 0-8 millim. wide. These give ofi: branch-canals 0*16 

 millim. wide. The stout stems are pretty regularly perpendicular to the surface, 

 the branch-canals irregular. The ciliated chambers are spherical, 0'04o millim. 

 wide, and destitute of special efferent canals ; they open directly into the 

 exhalants, which join to form larger stems 2-3 millim. wide, which extend 

 upward and inward, and cross the fascicles of main fibres at nearly right angles. 

 It is clear that in this case the direction of the main fibres is not parallel, or 

 even adapted to that of the large canals, as it is generally assumed to be. The 

 ciliated chambers have very small, under ordinary circumstances imperceptible, 

 afferent pores. There are no large apertures connecting the inhalant canals 

 with the ciliated chambers, as represented by Polejaeff in plate v. fig. 3 of his 

 ' Challenger ' Eeport on Keratosa. The large exhalant stems open out into 

 the wide centrally situated oscular tube, in which annular strictures are 

 observed. These are particularly highly developed in S. a. conulata, where 

 they often extend to form veritable sphincter-membranes. The oscular tube of 

 S. a. fovea, on the other hand, is pretty smooth. 



I have observed in the membranes dividing the canals of the subdermal 

 system very abundant large granular cells, particularly in S. a. conulata. The 

 ova mature in endothel-capsules, which are situated in the meshes of the 

 fascicles of main fibres. 



I divide this species, the conception of which in this extent is new, into 

 six varieties, among which several sponges previously described by Carter, 

 Hyatt, and Polejaeff, as Cacospongia and Stelospongos, are distributed. To two 

 of the varieties no previously described sponges appear referable. The species 



