new Genus of Devomcn Corals. 395 



series of such specimens as those above mentioned have led 

 lis to the conckision that they consist, as a general rule at any 

 rate, of two or more colonies of a single species in different 

 states of preservation. 



The principal grounds of a general nature upon which we 

 base this conclusion are as follows : — 



(1) Very many specimens are composed of successive 

 layers, which may or may not be separated by complete 

 interruptions of their continuity, but which must belong to a 

 single species, as being throughout identical in structure. 



(2) When successive colonies differ in apparent structure, 

 they for the most part agree nevertheless in the size of the 

 corallites, and they only differ as to the extent to which the 

 walls and visceral cavities of the corallites have been oblite- 

 rated by the induction of a peculiar secondary alteration, which 

 we shall show to be due to mineralization. 



(3) In the few instances in which the tubes in successive 

 colonies not only differ in apparent structure, but also in size, 

 the latter difference is not greater than often obtains in diffe- 

 rent parts of a single layer, or of successive layers which 

 otherwise agree in every respect. 



(4) In these composite specimens the different layers are 

 all precisely conterminous, each being applied to the entire 

 surface of the layer below. If, however, we were dealing with 

 a case of the parasitism of one species upon another, we could 

 not fail to meet with specimens in which the parasite would 

 only partially envelop the organism upon which it grew. 



We consider then that the differences in apparent structuye 

 above alluded to constitute an individual and not a specific 

 character, and we shall consider the nature of this character 

 immediately. Before doing so, however, it is advisable to 

 make some remarks upon the size of the tubes in the present 

 species. The diameter of the corallites is a point to which 

 Schliiter assigns a specific value, and upon which he lays 

 considerable stress. Thus he assigns 20-22 tubes in a square 

 millimetre to Ccdamopora piliformis, Schllit., this correspond- 

 ing roughly with a diameter of between | and i millim. to the 

 individual corallites. Galamopora slromatoporoides^ Roera., is 

 said to have 30-40 tubes in a square millim., which would give 

 a rough average of from rather less than \ to rather more than ^ 

 millim. Galamoporacrinalis^ Schliit.,is stated to have 14 tubes 

 to the square millim., which would give a diameter of rather 

 less than \ millim. to the individual corallites. Lastly, 

 Pachytheca stellimicans, Schliit., is stated to have 12-15 tubes 

 to the square millim., or a diameter of between ^ and 5 

 millim. to each tube. 



