238. PERCY SLADEN TRUST EXPEDITION 



variety about to be described, that the trichodragmata occur in the cortex as well as in 

 the choanosome. I therefore think that Dragmastra is the genus to which Stelletta 

 lactea must be assigned. 



6. Dragmastra lactea (Carter) var. mauritiana nov. 

 (Plate 46, fig. 7.) 



Stelletta lactea Carter [1871 a]. 

 Stelletta lactea Norman [Bowerbank 1882]. 

 Pilochrota (?) lactea Sollas [1888]. 

 Pilochrota lactea Topsent [1894 g]. 

 Stelletta lactea Lendenfeld [1903]. 



Mr Carter originally described this species from the coast of Devonshire, and stated 

 that it is " massive, spreading, fixed, following and filling the cavities of deciduous 

 small boring shells (SaxicavcB) and Annelids, which confine themselves to the surface of 

 the sandstone rock in which they live, almost entirely concealed by overgrowths of small 

 Cirripedes and Fuci, and communicating with the exterior only through the openings 

 of the cavities mentioned." 



It is very interesting to find a closely related form, obviously a variety of the same 

 species, adopting a similar " cryptozoic " mode of life at Mauritius. 



The single specimen forms a thin crust, growing upon a horny sponge (R.N. cxxvi. 4) 

 beneath a specimen of Latrunculia (R.N. cxxvi. 4 c). The main skeleton consists of 

 dichotrisBnes and oxea ; the dichotrisenes being mostly arranged in loose brushes with 

 their cladomes just beneath the surface, while others are irregularly scattered in the 

 deeper parts of the sponge. A few of the oxea are radially arranged, but most of them 

 seem to be irregularly scattered, singly or in bundles. 



Spicules: — (1) Dichotrisenes (Plate 46, fig. 7 a) ; shaft short and stout, gradually 

 sharp-pointed, characteristically bent somewhat to one side at about one quarter of its 

 length below the cladome, measuring about 0"4 by 0'0258 mm ; cladi very short, each 

 bifurcating into two short, sharply conical branches about equal in length to the main 

 branch; total diameter of cladome about 0"1 mm. A few much more slender trisenes, with, 

 unbranched cladi, also occur ; these I take to be young forms of the dichotriaenes. 



(2) Oxea (fig. 7 h) ; nearly straight, fusiform ; gradually and fairly sharply pointed ; 

 measuring about 0"75 by 0'02 mm., but frequently more slender. 



(3) Oxyspherasters (fig. 7 c) ; very minute, sometimes with well-developed centrum 

 and numerous very slender rays about as long as the diameter of the centrum, but the 

 proportions are variable ; total diameter about 0"008 mm. Especially abundant in a 

 superficial layer. A few (fig. 7 d) occur as much as 0"016 mm. in diameter, usually 

 with long, slender rays and relatively small centrum. 



(4) Trichodragmata (fig. 7 e) ; very numerous in some parts of the sponge, rare 

 in others ; measuring about 0'02 by 0"004 mm. 



The small size and general condition of the sponge do not allow of my saying much 

 about its minute anatomy or histology. There is no distinct fibrous cortex, but there 

 appears to be a thick gelatinous ectosome (about 0'86 mm. thick), distinguished by its 

 lighter colour and clearer appearance from the underlying choanosome. 



