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



Nephthyidse of a very various form, but with the barren trunk always exhibiting a 

 greater or less degree of development. The polyps are not retractile ; their little heads, 

 beset with large spicules, have a firm consistency and are overtopped by bundles of large, 

 spindle-shaped spicules, which project like spines all over the colony. In the walls of the 

 little heads the spicules are mostly placed obliquelj^, at the base of the tentacles they 

 are arranged in a ring. The tentacles themselves are beset with spicules arranged 

 en chevron. The walls of the polyp tubes and of the larger cacals of the stem and 

 branches are thin and fleshy ; the surface of the colony, on the other hand, is hard and 

 stiff, owing to the presence in the coenenchyma of numerous, spindle-shaped spicules. 



The polyps are placed on the branches and twigs, several may be united in one 

 bundle or they may be isolated and scattered. Gray [loc. cit.) attempted to base two 

 genera upon this character, which he distinguished as Spoggodes, with the polyps united 

 in bundles, and Spoggodia, with isolated polyps. 



Verrill {loc. cit.) showed, however, that in certain species, e.g., Spongodes gigantea, V., 

 both characters are present in one and the same colony, so that the generic separation 

 attempted by Gray falls to the ground. 



The genus Morchellana, made by Gray {he. cit.), must also, according to Ridley, 

 who investigated the type,^ be united with Spongodes. 



For a long time only four species of the genus were known, viz., Spongodes Jlorida 

 { = Alcyonium Jloridum, Esper), Spongodes celosia, Less., Spongodes arhorescens, Dana 

 (Verrill), and Spongodes savignii, Ehrbg. The first three were regarded by Gray as 

 synonymous with Spongodes Jlorida, Esper, but nevertheless they must be considered as 

 distinct species. In 1862 Gray addfed, from the material in the British Museum, four 

 more species (five if we count Morckellana). In January 1864^ Verrill described two 

 new species, Klunzinger {loc. cit.) made two, and Ridley one,^so that at the present day 

 the number of known species reaches fourteen. The collection made during the voyage of 

 the Challenger contains twenty-two species, of which eighteen are new to science ; if we 

 add to these the six new species collected by Dr. Doderlein in Japan, and also the two 

 new species mentioned below, the number as yet known reaches forty species {vide review 

 of species, p. 225). 



This great multiplicity in the development of the generic type appears to be due to 

 the fact that most of the species inhabit shallow water, commonly the declivity of coral 

 reefs, where the isolation of individual forms is greater, and at the same time the 

 external conditions of life are subject to greater change, than in the case of the 

 inhabitants of deep water. The same phenomenon is here repeated as in the case 

 of the genus Madrepora. Most of the species are found within the tropical zone, at 

 depths of from 10 to 70 fathoms, few range down to over 100 fathoms. 



' Ann. and ^fag. Nat. Hist., ser. 5, vol. ix. p. 186, 1882. - Bull. Mus. Com])- Zo'ol, vol. i. p. 39. 



' Zoology of the Voyage of H.M.S. " Alert," p. 333. 



