110 Mr. J. D. Dana on Zoophytes. 



tical, that the separation can be sustained only on the ground of 

 convenience in a distribution. We add, that in this last-men- 

 tioned case the simple species pass as gradually into the com- 

 pound, and they are closely connected with the group Euphyllia, 

 D. (a part of Lobophyllia, Bl., having entire lamellae). 



6. Growing massive , or calicularly branched (aggregate or 

 segregate), is sometimes a good generic distinction. But polyps 

 in contact grow together so readily that it can be of importance 

 only when supported by other characters. In the group Mani- 

 cina no line can be drawn between the segregate and coalescing 

 species; and the Cyathophylla are other examples. Difficulties 

 in the way of characterizing groups thus arise, which must be 

 fairly met and not denied nor overlooked. 



7. The forms of growth, whether branching, massive or ex- 

 planate, afford good distinctions for species, but seldom generic 

 characters. We find explanate and massive Gemmiporse and 

 Porites; explanate, massive and branching Porites and Mano- 

 porse ; and explanate and branching Merulinse and Echinoporse. 

 No more unfortunate generic character can be laid down than one 

 drawn from this source : it may, however, be occasionally used 

 when sustained by other characters. The genus Explanaria of 

 Lamarck is an agglomerate of species of several genera. 



We have elsewhere shown that the sizes of branches, the fre- 

 quency of branching, and the width of intervals in groups be- 

 tween branches, are good trivial characters within certain limits. 

 But in all cases in instituting species, the specimens examined 

 should be good and full-grown, and not fragments. 



8. Growth by budding from an apical polyp, or from serial 

 budding, are points that may afford good generic distinctions. 



IV. Tentacles and General Character of the Exterior. — In 

 many genera the tentacles are too short to take any part in the 

 prehension of food, and apparently subserve only the purpose of 

 aeration. As the whole body takes part in this function, the size 

 of the tentacles must necessarily be unimportant as a family 

 character. Hence we find, even in the same genus (Fungia, 

 Porites), species with comparatively long tentacles, and others in 

 which they are almost obsolete. The species of the genus Ac- 

 tinia are almost as various in the sizes of the tentacles. Among 

 the AstrcEce, one species was observed by the writer in which the 

 place of tentacles was supplied by numerous spine-like processes 

 over the surface between the discs ; and the same is true of the 

 Echinoporce, or at least partly so, for the writer observed no ten- 

 tacles in the two species he examined. The same reason shows 

 that the moss-like subdivision of tentacles, observed in some Ac- 

 tinida,, is a character only of generic importance, for it takes place 

 generally in such species as live more or less buried in the sand 



