ratoisidinae enenchyma thin; calyces inserted, long, usually cylindrical; characterisüc 



spicules in the form <>f spindles, or flattened bar like of hour-glass forms \\ hich are smooth 



i>r with minute spiny points, never with true verrucae; colonj not profusely branched. 



setnac enenchyma thin; calyces usually exserted; often club-shaped; characteristic 



spicules flattened scales, uiten profusely branched or ctenate on their edges. 



Systematic relationships ol the family Isnu. 



The closesl affinities of this family seem to be with the Primnoida, a fact which has heen 

 commented upon- 1>\ several writers, the calcareous internodes of the former being appanntK 

 very similar in composition and structure to the calcareous axis of the latter. The ccenenchyma 

 is usually thin in both families 



In the polyps and calyces >>( certain Isida we have a very strikin^ similarity to those of 

 the Primnoida, and this is particularly true in the case of tlie new genus J'eltastisis described 

 in this Report. Here the form ut' the calyx, the form and arrangement of the spicules, the 

 reduction in the number of adaxial scales, and the essential character of the uperculum (a scale 

 t" each segment) are all typically primnoid in their nature. Werc it not for the jointed axis 

 *<( Peltastisis 1 doubt il" any one would hesitate in putting it in the family Primnoida. 



Indeed the character of the axis alone can be successfully used in separating these two 

 closely related families. 



( m the other hand, the Isida show many characters in common with the sclerogorgian 

 family Melitodida. These families can not be separated on the characters of the spicules, for 

 those of the Isina show the same general characters as are common in the Melitodida-. The 

 nodes and internodes are superficially much alike in the two families, and the calcareous inter- 

 nodes are in some cases, particularly in the older parts of the colony, apparently almost as 

 completely calcareous and amorphous in the Melitodida as in the Isida. It was formerly held 

 that both nodes and internodes of Melitodida- were penetrated by solenia ; hut this is now 

 denied '. Here, again, the characters of the axis seem to afford the only reliable means of 

 family differentiation, the horny nodes of the Melitodida- being always more or less mixed with 

 calcareous spicules, while those of the Isida are purely horny, without spicules. 



I he writer desires to emphasize an opinion elsewhere expressed '- as follows: 



*( )ur knowledge of the lower invertebrates is still far too fragmentary to permit us to 

 indulge the hope that our work as systematists will really serve to express in final form the 

 actual relationships of any large group of animals. 



\\ hile a natural classification is a 'consummation devoutly to be desired' we are not yet, 

 it seems to me, in sight of it". 



The main service of classification, in our present state of knowledge, is to facilitate 

 itification of groups, the final result being facility in determination of species. 



\ Treatise on Zoology. Part II, Chaptet VI, p. 2S. 191 



I >n, Hl The MuriceicUe, 1900, p. g. 



