s!tiiuci'tJRE Of isIs Hip:PUKis. 423 



Dana, in his 'Zoophytes,' 1846 (XIX.), tljus limits the genus : — 

 " Isinae consisting of corneous and calcareous joiuts alternately ; 

 branches proceediug from the calcareous joints ; cortex thick, 

 deciduous." 



In 1857 Milne-Edwards & Haime (XXII.) recapitulate the 

 genus in the following terms : — " Colony with axis alternately 

 calcareous and horny ; calcareous portions sclerobasic, varying 

 n length according to the specimen and having horizontally 

 disposed ridges straight or bent ; branches borne on the calcareous 

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

 established by Steeustrup, viz. /. polyacaniha and /. monili- 

 formis^ as well as to the older species /. coralloides (Lamk.) and 

 I. elongata (Esj^er). 



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

 taken of the spiculatiou ; but in the ' Proceediugs of the Zoological 

 Society,' 1857, Gray gives the following important though in- 

 definite amendment : — " 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 liamarck's " caduce en totalite " 

 (2) sometimes the horny parts become obliterated by an exces- 

 sive growth of the calcareous portion, and this may account 

 for Lamarck establishing the genus Cynosaire (Mem. Mus. 

 Hist. Nat.). 



In the same work Grray also established the genus Isidella, 

 into which he merged no fewer than four of Lamarck's species of 

 Isis; and at a later date (1887) Gr. von Koch changed his Isis 

 neajpolitana to Isidella neapolitana. The following is Gray's 

 diagnosis of Isidella : — " Coral branched, furcate. Axis smooth, 

 cylindrical ; stony joint elongate ; branches furcate, proceeding 

 from the corneous joint. Bark rather thick, with irregular 

 opake spicula ; polypiferous cells produced, subcylindrical ; 

 base o£ axis expanded, lobed and branched." 



The genus under consideration has thus received its position 

 from the nature of its axis, with but indefinite knowledge of 

 cortex, polyps, and spicules ; but in 1865 KciUiker, in his ' Icones 

 Histiologicae,' rendered this part of the work more precise by his 

 introduction of a more definite spicular basis of classification. 

 The following gives. precisely his important addition : — "I know 

 only the spicules of the coenenchyma of 1. hippuris, which 



