PORIFERA. I. 21 



the skin outside the dermal reticulation, and form, especialh- where no reticulation is found, a dense 

 la\er in the outermost part of the skin; they are further found in the membranes that bound the 

 canals and cavities, and these membranes have often chiefly these smaller spicules, while the_\- do not 

 seem to form part of the fibres. 



It is with some hesitation that I have determined this species as H. fibrosa, although I have 

 had one of the original specimens of Fristedt for comparison. They agree, however, as to form 

 and structure, the fibres have the same degree of development, and the dermal layer shows also in 

 some places reticulation, in others closely packed spicules. The spicules also fall into two groups, but 

 the larger ones are somewhat differing from the spicules of my specimens; the\- are finer, reaching 

 onlv a thickness of o'Oii""", b>' which fact the difference between the smaller and larger spicules 

 becomes less marked; further the>- are often more strongly and more irregular!}- curved, and often 

 longer pointed; Fristedt, who does not mention two .sizes of the .spicules, states their length to be 

 0-5 — o-g™'", and declares the latter length to be the more frequent; it is to be supposed that an error 

 has taken place in the measuring, as the greatest length measured by me in the specimen of Fristedt 

 before me, is o-sg""'"; nor does the figure of F'ristedt agree with what I have ob.served; the spicule 

 pictured b\- him in fig. 11, is far too long tapering and recalls the spicule of H. pa-jiicea, while the 

 .spicules of the .specimen sent to me, are almost altogether more shortly pointed; finally must be men- 

 tioned that spicules with a swelling are also foiuid in the specimen of Fristedt. The .smaller .spicules 

 agree in form and structure with those in my specimens. According to this I must regard my speci- 

 mens as belonging to this species, and especialh', as also the thickness of the large spicules appeared 

 rather varying in m\- specimens. 



Locality. West-Greenland; we have two glasses from an earlier time, one without any nearer 

 localit)- gi\-en, the other from Proven. Later the species has been taken on Ikertokfjord, depth 30 

 fathoms (Th. Holm). 



Geogr. distr. Like the preceding species this latter one is onl\- known as arctic; besides in 

 West-Greenland it has been taken in the Behring-Strait, depth 25 fathoms (Fristedt I.e.). 



Note. As we have seen, these two species, H. genitrix and fibrosa belong to the group of 

 Balic/ioiidria-s^&c\&s having spicules of two sizes; the smaller spicules here correspond to those which 

 Bowerbank calls tensioji spicula\ and as species, in which tension spicula are different from 

 skeleton spicules, we find in Bowerbank: Hynieniacidon Thomasii. Brettii. fragilis. lactca^ Halichon- 

 dria inconspiciia, incerta and editsa\ it will, however, only b\- an examination of original specimens 

 be possible to get a sure idea of these species; as has been mentioned under H. paiiicea, Hymoiiacidon 

 Tlwniasii and Halichondria incerta are perhaps synonymous with tliis species. Fristedt (op. cit. I\ , 

 424) mentions a species, Aiiiorphiiia renieroides, a piece of which I have liad for examination; the 

 spicules of this species, var\ing from 0-15 — o-G""", remind of the spicules in genitrix, but it seems to 

 be distinguished from this species by the fact that the spicules are thicker and not so long tapering, 

 and besides, otherwise contrary to the observations of Fristedt, con.siderably thicker than the small 

 .spicules of the species; it is likewise distinguished from genitrix by the fact mentioned by Fristedt, 

 that the outermost spicules are more or less perpendicular on the surface. 



V 



