512 " THETIS " SCIENTIFIC RESULTS. 



This species is described with some hesitation, but the spicular 

 characters differ considerably from those hitherto known, both 

 in arrangement and in dimensions of the spicules. 



SIGMAXINELLA, Dendy. 



SIGMAXINELLA MAMMILLATA, sp. nov. 



(Plate xlvi., fig. 39.) 



Station 15, 



Sponge consisting of about ten mammiform processes, arising 

 from a well developed base and a short peduncle ; the branches 

 are coalescent in their lower three-fourths, but mostly free at the 

 summits. The example is 70 mm. high, 75 mm. wide, and about 

 40 mm. in thickness. The free apices of the branches vary from 

 15 to 25 in height and are generally 15 mm. in diameter. The 

 surface has a thin epidermal la3'er provided with numerous 

 minute pores about 0'5 mm. or less in diameter; these are more 

 or less connected by a series of small radiating grooves ; the 

 pores are from 1 to 1 "5 apart and are evenly distributed over the 

 whole sponge. In places where the dermis has been abraded the 

 surface presents a velvet-like aspect. The summits of the well- 

 rounded or sometimes slightly compressed branches bear from two 

 to seven oscula f I'om 1 to 1 5 or 2 mm. in diameter ; interspersed 

 between the oscula apertures are a series of subradiating grooves 

 0"5 wide, and extending down the sides for a distance of 5 mm. 

 or more. 



Texture rather hard, tough, and resilient ; colour yellowish- 

 brown. 



Skeleton composed of a series of somewhat diffuse primary 

 and secondary fibres; the foraier are from 0-3 to 0*5 mm. in 

 diameter, and consist of ill-arranged spicules imbedded in much 

 yellow spongin ; the latter are better defined ; they are about 

 0-1 to 0-15 mm. in diameter, and the spicules are arranged in 

 axial lines of six or more, with a series of echinating spicules 

 placed at rather acute angles, and finally terminating in radiating 

 tufts at the surface. The secondary fibres are mostly given off 

 at right angles to primaries, and here and there connecting fibres 

 are present containing one or two spicules. The length of the 

 latter indicates the distance between the fibres. 



Megascleres : — styli with a straight shaft tapering to an acute 

 point ; the base is usually bent about two or three diameters 

 from its well-rounded extremity; size 0*25 to 0-28 by 0-015 to 

 0-018 mm. 



Microscleres : — sigmata, 03 by 0025 mm. 



