tJie Genus Fistiilipora, M^Coy. 503 



hj fission. In tangential sections the mesopores often exhibit 

 a septura-like process extending to a greater or less distance 

 into the cavity of the tube. This phenomenon, so well known 

 as occurring in the genus ChceteteSj Fischer, is the result of 

 the fissiparous development of the corallites. We have ob- 

 served precisely similar phenomena in the mesopores of 

 Constellaria antlieloidea^ Hall, and in the autopores of Mono- 

 trypa pulchella, E. & H. In our opinion this fissiparous 

 mode of development is a strong argument in favour of the 

 reference of these forms to the Actinozoa rather than to the 

 Polyzoa. 



In the earliest stages of growth F. incrustans forms thin 

 suhcircular crusts upon foreign bodies, each crust commencing 

 with a single " macula," from which the corallites radiate. 

 In the progress of growth fresh " macules " are formed, and 

 the crust gradually spreads over the invested body. In older 

 colonies the original crust becomes thicker by the gradual 

 elongation of the corallites in a direction at right angles to the 

 invested surface. Sometimes also there may be a temporary 

 cessation of growth, and then a second layer of corallites is 

 formed above the old one. At the point where the corallites 

 are attached to the body which the colony invests they are 

 slightly bent, in a fashion which occurs in all the Monticuli- 

 porid^ as also in all the Favositidse, where the colony springs 

 from an extended surface, whether this surface belong to an 

 invested foreign body or whether it be the na.tural epitheca. 

 The obliquity of the young corallites thus produced is ren- 

 dered in F. hicrustans apparently greater than it really is, 

 owing to the arching of the lips of the aperture of the auto- 

 pores on one side. As growth proceeds the corallites become, 

 however, quite erect. Even in the youngest colonies the 

 existence of both the autopores and the intervening meso- 

 pores may be recognized quite clearly. Nor is there any 

 diiference whatever in the internal structure of young and old 

 colonies ; the only distinction, in fact, between the earlier and 

 the later stages being merely the slight obliquity of the coral- 

 lites of the former. 



There seems to be little doubt that the fossil which M'Coy 

 described {loc. cit.) under the name of Berenicea megastoma 

 was really a specimen of the young stage of Fistulipora 

 incrustans. As before remarked, however, it is not possible 

 to be absolutely certain of this without an examination of 

 McCoy's original specimen, especially as M'Coy's figure of 

 Berenicea megastoma does not exhibit any mesopores, nor does 

 his description of the species contain any allusion to the 

 presence of " interstitial tubes." 



