PORIFERA. III. 



especially outwards, and in rather great numbers in the membrane forming the pore-sieves, and in 

 these places no sigmata occur; on the other hand, the chelae do not occur in the inner body, while the 

 sigmata are present here in enormous numbers, filling the tissue and also occurring everywhere in 

 the basal parts among the particles of the substratum. The consequence of this distribution of the 

 microscleres is that the sigmata are far more numerous than the chelse. 



Embryos. In one of the specimens, which was cut through, some embryos were found; they 

 reached to a diameter of 0-65 mm ; they smallest of them had no spicules, but the larger were richly 

 provided with microsclera, both chelae and sigmata; both forms were smaller than in the grown 

 sponge, the chelae 0-031 mm and the sigmata not surpassing o-o4O mm ; also in the embryo the sigmata 

 were far more numerous than the chelae. No megascleres were present 



Locality: Station 78, 6o37'Lat.N., 27 52' Long. W., depth 799 fathoms; station 84, 62 58' Lat N., 

 25 24' Long. W., depth 633 fathoms; station 90, 64 45' Lat N., 29 06' Long. W., depth 568 fathoms. In 

 all five specimens. The localities lie in the Denmark Strait and on the eastern slope of the Reykja- 

 naes Ridge. 



36. H. digitata n. sp. 

 PL III, Fig. 15, PL IX, Fig. 4. 



Incrusting or of somewhat massive appearance; surface smooth, bearing some thin oscular and 

 pore-papilla; the dermal membrane with horizontal spicules. Spicula: megasclera; the skeletal spicules 

 acanthostyli, divided into two groups, large, without a distinct head and not entirely spined, 0-25 0-31""", 

 small, with a distinct head and entirely spined, o-n 0-14"""; the dermal Spicules tylota 0-26 0-4 17""*; 

 microsclera two forms, chela arcuatce 0-034 0-038""", sigmata 0-028 0-050""". 



This species resembles the preceding in outer appearance, but the specimens present are small; 

 we have only two specimens, growing on stones together with other species of Hymedesmia and some 

 other incrusting sponges. The sponge forms a basal, incrusting or more massive part, from which a 

 number of long, thin papillae issue; in the present specimens the number of papillae does not exceed three; 

 they are of the common shape and reach to a length of 7 mm . As said the specimens are small, the 

 basal part has a greatest extent of about 5 mm . The colour (in spirit) is yellowish or whitish. The 

 surface is smooth, and the dermal membrane constructed as in the preceding species. Oscula and pores 

 are connected with the papillae quite as in the preceding species. 



The skeleton. The dermal skeleton; the skeleton formed of the dermal spicules consists of 

 more or less distinct fibres going from the basal skeleton towards the dermal membrane; in the 

 membrane the spicules lie horizontally, and they are as usual lying close in the wall of the papillae 

 in the longitudinal direction, intercrossing at acute angles. The main skeleton consists of basal acantho- 

 styli with their heads on the substratum. Spougin is present, but only to a very slight degree. 



Spicula: a. Megasclera. i. The skeletal spicules are acanthostyli; they are divided into two 

 rather distinct groups, large and small; the large styli are slightly curved, they are thickest at the 

 base but without any real head-swelling; they taper evenly but the outermost point is short, and they 

 are spined in somewhat more than the basal half; the spines are small, only at the base a little 

 larger. The small styli are straight and have a distinct head, the shaft is beset with relatively large 



