SPONGES — WHITELEGGE. 459 



The " Thetis " collection contains a large series of fine 

 specimens of P. communis, and these, together with the rich 

 material in the Museum, afford ample examples for study. In 

 addition there are several fragments — taken from Lendenfeld's 

 collection now in the British Museum — which have been com- 

 pared with the rest of the material at my disposal. 



The result of the examination is a conviction that P. comviu7iis, 

 Ldf. — with its two varieties Jiabellum and digitata — P. elegans, 

 Ldf., P. elongata, Ldf., P. tenuifibris, Ldf., and P. seiyens, Ldf., 

 are forms of one extremely variable species. They differ slightly 

 in habit, density, and in the relative size and distribution of the 

 oscula. These characters are extremely variable according to the 

 habitat in which the sponge has grown, and the same remark 

 applies both to the fibrous skeleton and the spicules, There is 

 one feature they have in common, and that is the appearance 

 and structure of the dermal surface. These peculiar epidermal 

 characters can also be seen in P. pu7iciata, Ridley and Dendy, P. 

 pedtcncidata, Ldf., and, judging from the description, in Ghalina 

 monilata, Ridley. 



The dermal surface when well preserved is glabrous, velvet-like 

 in appearance, and coated with a thin crust of oxeote spicules ; 

 the latter are very closely arranged, and partly conceal the 

 dermal network as well as the pores, which are scarcely visible to 

 the unaided eye. The spicular measurements are as follows : — 

 Pachychalina communis, Ldf., " type," 0-06 to 0-08 by 0-0045 to 

 0*006 mm. In the choanosome there are a few 0"06 by 0002 mm. 

 P. communis var. digitata, Ldf., 0"06 to 0'07 by O'OOGmm, 

 P. com,m,unis \ar. JlabeUu77i,Lidi., 0-06 hy 0-006 mm.. P. elongata, 

 Ldf., 0'06 to 0-07 by 0-006 mm. P. elegans, Ldf., 0-065 by 0-0055 

 to 0-006 mm. P. serpens, Ldf., 0-06 to 0-08 by 0-0065 mm. in 

 choanosome, and 0-06 to 0-07 by 0*0045 mm. in skeleton fibres. 

 P. te^iuifibris, Ldf., 0-06 to 0-07 by 0-0055 to 0-006 mm. 



SIPHONOOHALINA, Schmidt. 



SIPHONOCHALINA ANNULATA, Ridley and Dendy. 



Siphonochalina annulata, Ridley and Dendy, Chall. Rep., Zool., 

 XX., p. 31, pi. vii., fig. 2. 



Station 48. 



A single example of this species is present in the " Thetis " 

 collection. The habit of the specimen is different from that of 

 the figured type. The form is more compact, and on one side the 

 whole of the branches exhibit coalescence for at least half or a 

 third of their length. The specimen is 224 mm. high, 140 mm. in 



