ON THE BRITISH SPECIES OF OEISIA, 121 



Habit of Zoarium at Different Seasons ; Begeneration. 



A very slight acquaintance with the British forms of Crisia 

 enahles one to distinguish at a glance, in most cases, the 

 species to which a given specimen belongs. C. denticulata 

 is characterised by the coarseness of its general habit ; by the 

 regular dichotomous appearance of the branching, as seen by 

 the naked eye ; and by the fact that the branches diverge from 

 one another to such an extent that they are separated from one 

 another by considerable interspaces at their ends. In C. 

 eburnea the branches are inflected towards the axis of the 

 colony, and are so closely massed together that it is impossible 

 to study the exact character of the branching without first dis- 

 entangling the branches. On flattening the specimen out on a 

 slide the cymose character of the branching is at once appa- 

 rent. C. aculeata possesses a characteristic delicacy of habit 

 ("of a slenderer habit than C. eburnea, which the species 

 closely resembles"^); and it may be compared, in external 

 form, to a C. eburnea which has become of much laxer and 

 slenderer habit than usual, and in which comparatively few 

 branches have been developed. The branches are much 

 straighter than in C. eburnea. C. ramosa is extremely 

 similar, in general appearance, to C. aculeata, but is of dis^ 

 tinctly coarser habit ; the branches are very straight, and the 

 number of the branches to which the internodes near the grow- 

 ing-points give rise results, in actively growing colonies, in the 

 formation of fan-like systems of branches. The long tubular 

 apertures of the zooecia (if developed) give a characteristic 

 appearance to the species, which cannot, however, in all cases 

 be distinguished by the naked eye from C. aculeata. 



The above remarks apply especially to colonies in their fully 

 developed condition; but the appearance of any species de- 

 pends largely on the time of year at which it was found. 

 Many of the specimens of C. eburnea found in the early 

 spring are provided with numerous ovicells, the ultimate fate 

 of which seems to have hitherto attracted no attention, although 

 » Johnston, G., ' A Hist, of the British Zoophytes,' ed. 3, p, 286. 



