312 NATURAL HISTORY OF 



is enveloped in a '' bivalve protective case," lias been 

 investigated by the Rev. Thos. Hincks, whose re- 

 searches may be found in the Annals of Natural 

 History for November, 1851 (ser. 2, viii., 357). 



FAMILY III. ARACHNIDIID^. 



Zooecia usually more or less distant, membranous. — 

 T. H. 



Genus Arachnidium, HincJcs. {apd-x^viov, a spider's 

 web.) 



Zoarium membranaceous. Zooecia usually separate, 

 distant, adnate, united by a more or less filiform pro- 

 longation of the cell wall, so as to form a delicate 

 network. — T. H. 



1. A. HiPPOTHooiDES, HincJcs. 

 Arachnidia hippothooides (T. H.). 

 Hab. : Isle of Man, Torbay (T. H.). 



In all the species of this genus the Hippothoan 

 habit of growth is displayed. The cells are ovate and 

 membranous, and are connected by long slender fibres 

 so as to have the appearance of network. A small 

 papilla marks the situation of the orifice. The branching 

 of the cells is arranged with great regularity. 



2. A. CLAVATUM, Hincks. 

 Arachnidia hippothooides {A. M. N.). 

 Hab. : Shetland [Jeffreys and Norman). 



A deep-water species, with the cells long and club- 

 shaped, and connected by fibres. The mode of reticu- 

 lation is much less regular than in the preceding 

 species. 



3. A. FiBROSUM, Hincks. 



