98 PORIFERA. III. 



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

 sizes, large and small; the large styli are slightly curved near the head which is only slightly thickened, 

 while the other end forms a long-pointed apex; the head and a short space above it are spined, while 

 the whole of the rest of the shaft and apex is smooth. The small acanthostyli are generally straight and 

 with the head still less thickened; they are more spined than the large, the spines covering the basal 

 half part or more, and the spines are relatively larger. The length of the large styli is 0-560-80""" 

 and the diameter of the head about o-o28 ram , of the small styli 0-21 0-30""" with a diameter of 0-021 

 0-025 """ 2. The dermal spicules are tylota; they are straight and the shaft is slender, the end- 

 swellings are distinct, but they are not formed abruptly but pass gradually into the shaft. The 

 length is 0-25 032 mm and the diameter of the shaft is 0-003 rara . Some few developmental forms were 

 found, the thinnest of them being monactinal. b. Microsclera are of three forms, chelae arcuatae and 

 sigmata of two forms and sizes, large, peculiar, and small, i. The chelae are of ordinary shape, the 

 shaft is evenly curved and the end-parts are relatively small; the tooth is elliptical and the alaa lobe- 

 shaped; the shaft is flattened, elliptical in section. The chelae vary somewhat in size, the length is 

 0-026 0-042 ram and the thickness of the shaft 0-004 o-oio mm ; with regard to the latter measurement 

 it must be remembered, that the shaft is about twice as thick when seen in front as when seen in 

 side view. The intermediate sizes of the chelae are scarce and hence they could be said to be present 

 in two groups of sizes. 2. The large peculiar sigmata are of a curious shape; they may be de- 

 scribed as having the curved end-parts somewhat long and terminating in a hook; they are contorted 

 generally a quarter of a turn, and the hooks are again bent a little out of the plane; but the most 

 interesting feature is that the rod forming the sigma is not cylindrical but compressed and thus 

 somewhat band-shaped. The size of the sigma from one curve to the other is 0-0280-035""", and the 

 thickness is O-QOI and 0-003 """ f r tne small and the large diameter respectively. 3. The small 

 sigmata are of ordinary shape and they are plane; the length is 0-0140-020""" and the thickness 

 about o-ooi mra . The chelae are present especially in the dermal membrane and rather numerous; the 

 two forms of sigmata are seen through the whole body. 



Locality: Station 78, 60 37' Lat. N., 27 52' Long. W., depth 799 fathoms; station 81, 6i44'Lat.N., 

 27oo'Long.W., depth 485 fathoms. In all three specimens. The localities are situated on the Reykja- 

 naes Ridge South-west of Iceland. 



43. H. mucronata Tops. 

 PI. X, Fig. 3. 



1904. Hymeraphia mucronata Topsent, Resultats des camp, scient. du Prince de Monaco, Fasc. XXV, 

 165, PL XIV, fig. 4 a-d. 



Incrusting; surface hispid. Spicula: megasclera; the skeletal spicules acanthostyli with no distinct 

 head, the larger spined at the base, the small entirely spined, 0-12 0-6 j mm , not divided into two groups ; 

 the dermal spicules fusiform oxytornota 0-22 0-268""*; microsclera three forms, chela of two forms, 

 ordinary 0-021 0-025""", peculiar, with some processes at each end, 0-021 0-026"'"', sigmata, large and 

 fine, 0-028 o- 



