REPORT ON THE MONAXONIDA. 11 



No doubt the Kerguelen specimen forms a connecting link, but we think it advisable 

 to distinguish between two closely allied species, Petrosia subtriangularis and Petrosia 

 similis, the former characteristic of West Indian seas, and the latter of the seas south 

 of the Cape. Two weU-marked varieties of the latter are described below, one of which 

 occurs as far north as the Philippine Islands. 



Localities. — Station 142, December 18, 1873 ; lat. 35° 4' S., long. 18° 37' E.; south 

 of the Cape of Good Hope; detph, 150 fathoms; bottom, green sand; bottom tem- 

 perature, 47°'0. Several specimens. 



Station 150, February 2, 1874 ; lat. 52° 4' S., long. 71° 22' E. ; between 

 Kerguelen and Heard Island; depth, 150 fathoms; bottom, coarse gravel; bottom 

 temperature, 35°'2. One small piece. 



Habitat. — South of the Cape of Good Hope (Challenger) ; Kerguelen (Carter) ; 

 between Kerguelen and Heard Island (Challenger). 



Petrosia similis, var. massa (PI. II. fig. 11; PL HI. fig. 6). 



Sponge (PI. III. fig. 6) massively lobose, or consisting of very stout cylindrical 

 branches. The largest specimen is a flattened lobose mass, which, judging from the fact 

 that it bears oscula on both surfaces, has probably grown erect; it is 162 mm. high 

 by about 50 in average breadth (narrowing from above downwards) and 18 mm. thick. 

 Colour in spirit greyish-yellow. Texture rather soft and spongy. Surface smooth 

 but uneven. Dermal membrane distinct, in parts with a lace-like reticulate appearance 

 owing to the supporting skeleton reticulation. Oscula large, circular ; irregulai-ly 

 scattered over the surface (yet with some tendency to form series) ; about 4 mm. in 

 diameter; commonly surrounded by a slightly prominent rim. Pores, rounded openings 

 in the dermal membrane as usual. 



This variety differs from the types in its more slender spicules, in the looser 

 skeleton arrangement and less compact and well-developed fibres (hence its soft, spongy 

 character), and in the more irregular arrangement of the oscula. The spicules (PI. II. 

 fig. 11) measure up to about 0-28 by 0-012 mm. The dermal membrane is not suj^ported 

 on projecting tufts of spicules, but rests dii-ectly upon a reticulation of spiculo-fibre, 

 which is, however, only the uppermost layer of the main skeleton. The character of 

 the dermal skeleton in th different species of Petrosia seems to be of very little use in 

 separating them. 



Locality.— Station 314, January 21, 1876; lat. 51° 35' S., long. 65° 39' W. ; 

 between the Strait of Magellan and the Falkland Islands ; depth, 70 fathoms ; bottom, 

 sand ; bottom temperature, 46°'0. Several specimens. 



