REPOET ON THE ALCYONARIA. 41 



recognise the retention of the genus Mopsea only for Mopsea encrinula} Kolliker in 

 his Icones Histiologicse apparently did not examine the typical Mopsea encrinula, and only 

 had Gray's Mopsella dichotoma and Ehrenberg's Mopsea erythraea, before him, which he 

 united with a new species under Mopsea. He refers Mopsea to the Melithseidse and 

 is therein followed by Klunzinger, who again only had Mopsea erythraea, Ehrenberg, 

 before him. 



It seems strange that de BlainviUe'* should not allude to this genus, though he 

 visited Caen in 1829 to examine the types of Lamouroux' species. 



The Challenger material contains both the species upon which Lamouroux founded 

 his genus, and supported thereby it is possible to restore the genus to its old condition. 

 The two forms which belong thereto are true Isidse ; the calcareous joints of their axis 

 consist of concentric lamellae with deposits of calcareous crystalline bodies. They retain 

 their essential form after treatment with acids. Together with the two new genera 

 Primnoisis and Acanthoisis they form a well-defined subfamily of the Isidae, that of the 

 Mopseinse, which are closely connected with one another through the form of the polyps 

 and of the spicules. 



1. Mopsea dichotoma (Linne) (PI. IX. fig. 10). 



Isis dichotoma, Linn., Syst. Nat., Ed. x. p. 799. 



„ „ Lamk., Hist. anim. sans vert, t. ii. p. 302. 



Mopsea dichotoma, Lamx., Hist, polyp, flexibles, p. 467. 



„ „ Milne-Edwards, Hist. Nat. des Coralliaires, t. i. p. 197. 



Non Mopsella dichotoma, Gray, Proc. Zool. Soc. Lond., 1857. 

 Nee Mopsella dichotoma, Verrill, Bull. Mus. Comp. Zool., 1864, p. 38. 

 Nee „ „ Kolliker, Icon. HistioL, p. 142, pi. xix. fig. 41. 



Stem upright, ramified ; the main stem, rising from a calcareous disk-like base, gives 

 ofi" slender branches on two sides at difiierent heights, which again develop lateral twigs 

 in similar manner. These are long and rod-like, and, arising at acute angles, soon turn 

 upwards and rise parallel to one another to about the same height. In this way twigs 

 are formed up to the fifth order. Since the twigs, arising from the stem or branches, 

 soon attain to nearly the same thickness, and the latter, at the origin of each branch, 

 is somewhat bent out of its straight course in the opposite manner, there arises the 

 appearance of a continuous dichotomy. The main stem, in the largest specimen, has 

 a diameter of 2 mm. at the base, and a height of 165 mm. The rod-like, unbranched, 

 terminal branches, may develop to a length of 95 mm. 



On the lower part of the stem the ccenenchyma is thin and allows the jointed axis 

 to show through, on the branches and twigs it becomes thicker and filled with polyps. 

 These, as Lamouroux has already asserted, are difi'erent on the thicker parts of the stem 

 and on the branches. On the thin branches they are projecting, club-shaped, with 



1 Proc. Zool. Soc Land., 1857, p. 283. - Manuel d'Actinologie, 1834. 



(zool. CHALL. EXP. — PAitT Lxiv. — 1887.) Sss 6 



