172 THE VOYAGE OF H.M.S, CHALLENGER. 



yet it must be borne in mind that there would appear to be no very well marked 

 distinctions between the warty spindles called " Stachelkeulen " by Kolliker and those 

 spindles with foliaceous tops, called by him " Blattkeulen." Sometimes the flattened 

 terminal crown of excrescences of a Stachelkeulen will be found to assume almost an 

 identity of shape with those of some of the attenuated " folia " of some Blattkeulen. 



It must also be remembered that there has been a great deal of confusion as to the 

 limits of the genera in this family, and even, as has already been pointed out, a misunder- 

 standing as to its leading characteristics, which date from the days of Linnaeus, and 

 which, from the impossibility of our obtaining many of the type species of Esper and 

 Lamarck, we cannot hope to have in every respect-cleared up. 



An examination of the species in the museums of Erlangen, Paris, and London, will 

 be needed ere many points in doubt can be cleared up. 



That the presence of a dense layer of " Blattkeulen " in the coenenchyma of such 

 species as Mopsella retifera (Lamarck), Mopsella coccinea (Ellis), Mopsella elongata, 

 Gray,' will easily distinguish them and allied species from most of those here referred 

 to Melitodes will not be contradicted. While this feature was already pointed out 

 by Kolliker, it assuredly never entered into Dr. Gray's conception of the genus 

 Mopsella. 



The distinctions also between the genera Acaharia, Gray, and Psilacahdria, Ridley, 

 seem not to be very well marked, but the time has not come for accurate limitation of 

 the various species, and in the meanwhile the following may stand as an emended 

 diagnosis of VerrUl's emended genus Melitodes. 



Colony adherent, branched ; branches very frequently in the one plane, but sometimes 

 ramifying in several planes. The main axis and the branches consist of soft (nodal) and 

 hard (internodal) joints, alternating. Branches proceeding (with few exceptions) from 

 the nodes, more or less freely anastomosing. Both nodes and internodes are formed by 

 sclerogorgic tissues, which become dense and more calcareous than horny in the inter- 

 nodes, and in the nodes remains more horny than calcareous, while the spicules are much 

 less consolidated together. The longitudinal canals penetrate both series of joints. The 

 coenenchyma varies much in denseness and contains an outer layer of spiny spindle- 

 shaped spicules (Stachelkeule) ; half-sided spiny spicules, these latter often very well 

 developed ; perhaps in the species of no genus is there to be found a greater diversity 

 in the form of the spicules, and owing to the manner in which they interlock with 

 one another, it requires some care to determine their perfect shapes. In the neigh- 

 bourhood of the verrucse spiny and bent spicules with spiny apices occur. The polyps 

 are retractile within more or less prominent verrucse. 



' This is not Mopsella elongata, Verrill. 



