xliv THE VOYAGE OF H.M.S. CHALLENGER. 



5. Isidella, Gray, Cat. Lithophytes Brit. Mus., 1870, p. 15. 



Isis, V. Koch, Morph. Jahrb., BJ. iv. p. 112. 



The colony is branched. The axis consists of long internodes and short nodes ; from 

 the latter the branches are given off. The eoenenchyma is furnished with small acicular 

 spicules with a few small spines. In the walls of the polyps the acicular spicules are 

 large with small spines; the largest are to be found between the bases of each pair of 

 tentacles, but only project beyond these in the dried specimen. The tentacles contain 

 small spindle-shaped spicules, which extend into the very pinnae. 



This genus is very nearly related to Acanella, but differs in the more spiny character 

 of the spicules and in the mode of branching. Gray referred four species to' this genus. 

 Uf these Isis neapolitana, v. Koch { — Mopsea mediterranea, Risso, = ilfop.^^ea elongata, 

 Phil., and doubtfully Isls elongata, Esper) has been carefully investigated by v. Koch. 

 This form may be regarded as the type of the genus. To judge from the nature of the 

 axis, which alone is known, it is possible that Isis gracilis, Lamrx., also belongs here ; 

 whether this is also true of Isis coralloides. Lam. , is doubtful. 



6. *ScZe?7Sis, .Studer, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1878, p. 661. 



The colony is upright and branched, with long finely-furrowed internodes and short 

 disc-shaped nodes. The branches spring from the internodes. The eoenenchyma is 

 very thin and without spicules. The calyces are bell-shaped, with constricted bases, and 

 are covered with large, curved, spinose spicules, which lie closely approximated. Over the 

 oral region of the polyp the large spicules form a quasi operculum. The genus forms a 

 transition towards the next subfamily. 



Subfamily 2. Mopsein^. 

 Mopseidx, Gray (pars). 



The colony is branched, the polyps, which are cup- or club-like, or cylindrical in 

 shape, have the tentacles folded over the oral region when at rest. The axis consists of 

 alternate calcareous internodes and horny nodes ; the branches spring for the most part 

 from the former, but sometimes so much on the upper border thereof, that the branch node 

 comes into contact with the stem node, giving the appearance as if it arose therefrom. 

 The spicules of the eoenenchyma are elongated and flattened with very zigzag dentate 

 margins. These dentations mutually interlock, bringing the adjacent spicules into 

 intimate contact. In the polyps the spicules are transversely disposed, and conform to 

 the outline of the polyp wall. In the tentacles there are usually three longitudinal rows 

 of spicules. 



This subfamily contains the following genera, of which the first, Primnoisis, seems 

 allied to Dasygorgia. 



