228 



MR. S. O. RIDLEF ON ALCTONARIA 



we have not many data. The genus does not appear to have been 

 recorded from the Atlantic and its outlying waters ; it seems to 

 be exclusively, or almost exclusively, tropical. 



All the species here to be described belong practically to that 

 cytnosely-pinnate section of the genus in which the zooids are 

 closely aggregated near the ends of the branches, the first of the 

 groups or subgenera (distinguished as Spoggodes) into which Dr. 

 Gray, in his useful paper in Proc. Zool. Soc. 1862, p. 27, divided 

 those species which were in the National Collection at the time at 

 which he wrote. The two species placed by him in that group are 

 S.florida (Esper), and$. spinosa, described for the first time. Of 

 these two species the latter is the most closely related to the 

 three species to be described below, from the cymose arrangement 

 of the terminal lobules. It is, however, readily distinguished 

 from all of them by the very large terminal spicules and their 

 grouping into very evident spine-like processes. A specimen in 

 the Museum identified (but probably wrongly) by Dr. Gray him- 

 self with his species, wants these processes, and has the terminal 

 lobules much more closely aggregated than in the type of the 

 species. It is probably closely related to one of the species 

 here described. 



8. Studeri, mihi (Eeport Zool. Coll. H.M.S. 'Alert,' p. 333), 

 belongs to the same circle of species, uniting the smaller spicules 

 of our species with that more scattered condition of the terminal 

 lobules which characterizes S. spinosa. Of other authors' species, 

 S. capitata, Verrill, evidently belongs to the same group. It is, 

 however, very difficult to identify species with authors' descrip- 

 tions, as they mostly show a great want of minute detail. 



Judging by the condition of their rooting-filaments, the Mergui 

 species prefer a sandy or gravelly bottom. The specimens in this 

 collection are commonly inhabited by Crustaceans, apparently 

 shrimps of one or more species, which are found wedged in 

 between the branches of the head. 



Si'ONooDEs aurora *, n. sp. (Plate XVII. figs. 20-24.) 



Capitate, with very short stalk; rather compressed from 

 back to front. Stem expanding immediately below head into 

 a largo fleshy mass, which gives off towards the surface short 

 broad-surfaced lobes which rapidly divide and subdivide, forming 



outwardly-flattened (tometimei slightly convex) lobules of angular 



* " Rokv fingered morn," from the delicate rosy tint which characterize* it. 



