PORIFERA. III. Q, 



the other hand densely filled with microscleres. When a vertical section is examined, the view is 

 therefore somewhat curious; in the interior foreign sponge-spicules are seen, and for the rest the 

 microscleres are predominant, filling the other space, the dermal spicules being only seen scattered 

 between the other elements, and it is only by close examination that an acanthostyle can be observed 

 here and there. The condition of the skeleton is, as seen below, due to the way in which the sponge 

 grows, and the principle of the construction is evidently the same as in the other species of Hyme- 

 dcsmia. There seems to be a little spongin at the base of the acanthostyli. On examining the 

 other specimens, which only came into my hands later, it proved, that the skeleton was here of the 

 ordinary construction and the styli were as usually placed on the substratum; otherwise it agreed with the 

 above description, the other space being occupied by dermal spicules and densely charged with micro- 

 scleres. Here also the styli of the skeleton were somewhat scarce and arranged very dispersedly. 

 It is of some importance to notice the facts with regard to these different specimens, as we see it 

 clearly proved here, that specimens of Hymedesmia may, when growing on loose material, assume a 

 shape and a manner of growth which may give rise to mistakes by influencing the arrangement 

 of the skeleton, though the construction of this latter is principally the same as in species of Hyme- 

 desmia growing on a flat and firm substratum. 



Spicula: a. Megasclera. i. The skeletal spicules are acanthostyli; they are straight and the 

 head-swelling is small or wanting; the spines on the basal part are somewhat large and close-standing, 

 on the rest they are small, reclined and few in number; the smallest styli are somewhat more spiued. 

 The length is 0-13 o-28 mm and the diameter at the head about 0-020'". 2. The dermal spicules 

 are straight, cylindrical strongyla or subtylota; the ends are generally swollen, but only to a very 

 slight degree. The length is 0-23 0-38 ram and the diameter is 0-0057 0-007 mm . b- Microsclera are three 

 forms, chelae arcuatse and sigmata of two sizes, i. The chelae are of the common shape, the shaft is 

 curved, the tooth elliptical and the alee lobe-shaped; they vary somewhat in size, the length is 0-020 

 0-032""" and the diameter of the shaft 0-0015 0-0028 mm . 2. The large sigmata are of ordinary form, 

 but somewhat elongated and generally only slightly contorted; they are of a considerable and very 

 uniform size, the length is 0-180-208""" and the thickness O-QJO o-oii mra . 3. The small sigmata 

 are of a less regular shape and they are contorted, generally a quarter of a turn or nearly so; their 

 length fe 0-06 0-089'""' an d the thickness 0-003 """. As said the microscleres occur in great numbers 

 all through the tissue; in the dermal membrane all three forms occur, but the chelae are here present 

 in greatest number and very close-lying. 



This species shows, in one specimen, a manner of growth quite as is found in grandis, and 

 it also shows resemblances to this species otherwise, but it is easily distinguished from it and 

 from the related species by the presence of two forms of sigmata. As seen from the description 

 I have not been able to decide whether the species in a more perfect state may be provided 

 with papillae. 



Locality: Station 54, 63 08' Lat N., 15 40' Long. W., depth 691 fathoms; station 78, 60 37' Lat N., 

 27 52' Long. W., depth 799 fathoms; station 89, 64 45' Lat. N., 27 20' Long. W., depth 310 fathoms. The 

 localities lie in the Denmark Strait and South of Iceland. 



