182 



Lamarck's " Hist. Nat. des Anim. sans Verteb.," 2ikI ed., 1836, vol. ii. p. 473, 

 thus defines the genus : " Colony attached, tree-like, composed of a jointed axis 

 surrounded by a cortex not cohering but deciduous. Axis central, erect, 

 branched, formed of calcareous striated nodes and horny constricted internodes. 

 The cortex bears polyps in the fresh state, but is totally or i)artially deciduous 

 when taken from the water." The writer discusses the question of relationship, 

 and from the presence of horny internodes suggests affinity with Go/yon/a and 

 Antipathes, in which, he remarks, the axis is not calcareous but entirely horny. 

 Brief notes on the following species are also given : /. hippuris, Linnseus ; /. 

 eloiigata, Esper ; /. dichotoma, Linnaeus ; 1. encrimda, Lamarck ; /. enralloides, 

 Lamarck ; /. gracilis, Lamarck ; /. erythracea, Lamarck ; and 1. melitensis, 

 Lamarck. 



Dana, in his "Zoophytes," 184(j (XIX.), thus limits the genus: " Isinse 

 consisting of corneous and calcareous joints alternately ; branches proceeding 

 from the calcareous joints ; cortex thick, deciduous ". 



Li 1857 Milne-Edwards and Haime (XXII.) defined the genus in the 

 following terms : " Colony with axis alternately calcareous and horny ; calcare- 

 ous portions sclerobasic, varying in length according to the specimen and having 

 horizontally disposed ridges straight or Ijent ; branches borne on the calcareous 

 portion ". At the same time they refer briefly to two new species established 

 by Steenstrup, viz., I. pohiamiitha and /. laonilifonnis, as well as to the older 

 species /. condhddes, Lamarck, and /. ehngata, Esper. 



It will be seen that, up to this point, no account has been taken of the 

 spiculation ; but in the " Proceedings of the Zoological Society," 1857, Gray 

 gives the following important though indefinite addition: "Bark thick, with 

 a few interspersed very irregular and unequal spicula ". His remarks on two 

 other points of structure are also very relevant and cannot be overlooked : (1) 

 that the bark is permanent and hard, but is brittle and easily removed, especially 

 if the specimens be kept in a dry place : hence Lamarck's " caduce en totalite " ; 

 (2) sometimes the horny parts become obliterated by an excessive growth of 

 the calcareous portion, and this may account for Lamarck establishing the 

 genus Ci/nomire (" M6m. Mus. Hist. Nat."). 



In the .same work Gray also established the genus IsideUa, into which he 

 merged no fewer than four of Lamarck's species of Isis. The following is 

 Gray's diagnosis of IsideUa : " Coral branched, furcate. Axis smooth, cylindri- 

 cal ; stony joints elongate ; branches furcate, proceeding from the corneous 

 joint. Bark rather thick, with irregular opaque spicula ; polypiferous cells 

 produced, subcylindrical ; base of axis expanded, lobed and branched." 



The genus under consideration had thus received its position from the 

 nature of its axis, with but indefinite knowledge of cortex, polyps and spicules ; 

 but in 1865 Kolliker, in his " Icones Histiologicai," rendered this part of the 



