AHACIINIDIUM niPPOTIIOOIDES. 509 



IN this genus the massive gelatinous crust, which cha- 

 racterizes the Alcyonidiida, is replaced by a membranous 

 zoarium. Arachnidium may be regarded as an Alcyo- 

 nidlum with its cells detached from one another and 

 held together by a slender thread, instead of being im- 

 mersed in a fleshy crust. Occasionally the cells are 

 massed together; but in general they are separated by 

 considerable intervals, and connected by a filiform exten- 

 sion of the lower extremity, branches being given off 

 from the sides. The habit of the Cheilostomatous genus 

 Hippothoa is curiously imitated by this form. 



ARACHNIDIUM HIPPOTHOOIDES, Hincks. 

 Plate LXXI. figs. 1, 2. 



ARACIIMDIA HIPPOTHOOIDES, Hincks, Dev. Cat., Ann. N. H. ser. 3, ix. 471, 



pi. xvi. fig. 2. 

 ARACIIHIDIUM HIPPOTHOOIDES (part.), Alder, North. Cat., Trans. Tynes. F. C. 



v. pt 3, 21 (sep.). 



Zocecia usually rather distant, ovate or lozenge-shaped, of 

 a light horn colour, connected by a slender fibre; orifice 

 marked by a small papilla near the top ; branches given 

 off from each side of the cell. Zoarium composed of 

 lines of cells, which anastomose and form a very delicate 

 network. 



IN this species the connecting fibre is generally well-deve- 

 loped, and the cells are separated by considerable inter- 

 vals ; their form is regular and definite. The branch 

 lines originate at different points on the sides of the 

 zooecia ; most commonly they occur in opposite pairs ; but 

 occasionally two are given off on each side; sometimes 

 they originate from the creeping fibre. The orifice is 



