1869.] Zoology. 573 



are chiefly remarkable for their sihceous spiculae, or skeleton, and 

 their wonderfully long and delicate pseudopodial threads, have long 

 been thought to have allies in fresh water, in the person of the 

 sun-animalcules (Actinojyhrys). But naturalists who have not 

 watched the record of the proceedings of the Dublin Microscopical 

 Club, published in the ' Quarterly Journal of Microscopical Science,' 

 will have been quite unprepared for the astonishing revelation of 

 several genera of these exquisite forms inhabiting the fresh-water 

 pools on the Irish moors. Their discovery is due to that careful 

 student Mr. William Archer. Dr. Focke, of Bremen, it is true, 

 has this year noticed the occurrence of some of these forms in 

 moor-pools in Germany, but Mr. Archer's notices are much earlier 

 in date than his, though his extended paper is only now appearing. 

 The largest form, which is a truly noble rhizopod, is as big as a 

 large pin's head, with thread-like pseudopods extending to a much 

 greater circumference ; masses of siliceous spicula are disposed over 

 the disc, which contains some dozen large spherical bodies of a 

 bright-green colour. This form Mr. Archer names B.ap}iidio])hrys 

 viridis ; other genera are characterized by Mr. Archer, and coloured 

 figures referred to. The chief point of difference between these 

 fresh-water Radiolarians and the marine forms is the absence in the 

 former of the central cyst or capsule, and the yellow cells which 

 have been considered of characteristic importance in the group. 



A Neiv Vitreous Sponge. — One of the products of the deep 

 dredging last year, in H.M.S. ' Lightning,' has been described to 

 the Eoyal Society, by Professor Wyville Thomson, as Holtenia 

 Carpenteri. It was dredged up from a depth of 530 fathoms with 

 several other organisms, there being four genera of Vitreous 

 Sponges. Holtenia is one of this new group of sponges, which 

 Professor Thomson makes to include also the Ventricuhtes of the 

 Chalk. The genus is named in honour of Mr. Holten, Governor 

 of the Faroe Islands. The order is mainly characterized by the 

 great variety and complexity of form of the spicules, which may 

 apparently, with scarcely an exception, be referred to the sex- 

 radiate stellate type, a form of spicule which does not appear to 

 occur in any other order of sponges. The genus Holtenia is nearly 

 allied to Hyalonema, and seems to resemble it in its mode of occur- 

 rence. Both genera live imbedded in the soft upper layer of the 

 chalk-mud in which they are supported : Holtenia, by a dehcate 

 range of siliceous fibres which spread round it in aU directions, 

 increasing its surface without materially increasing its weight ; 

 Hyalonema, by a more consistent coil of spicules, which penetrates 

 the mud vertically and anchors itself in a firmer layer. The 

 vitreous sponges. Dr. Thomson observes, along with the Hving 

 Ehizopods and other Protozoa, which enter largely into the com- 

 position of the upper layer of the clialk-mud, appear to be nourished 



