16 Dr Harmer on the Structure and Classification 



and others are to be regarded as branching Lepralioid forms. 

 Other Cellularine genera, e.g. Calwellia and Ichthyaria, are pro- 

 bably more nearly related to Microporella, although it is not 

 impossible that the median pore has been evolved more than 

 once. I agree with Waters in thinking that Ichthyaria cannot 

 retain its position in the family Bicellariidae. Urceolipora dentata 

 should perhaps be removed to Calwellia. " Euthyris " episcopalis 

 should be placed in a distinct genus, characterised in part by its 

 conspicuous ovicells, and the fact that both layers of their wall 

 are calcareous. Flustra militaris, Waters, appears to belong to 

 the same genus, and is probably a Lepralioid form in which most 

 of the calcification of the front wall has been secondarily lost. 

 The Lepralioid genera are probably to be arranged in two 

 divisions (see iv (a) and (&)), according to the manner in which 

 the calcareous front wall is developed. 



(viii) The calcareous matter of Cheilostomata is probably 

 always covered by an " epitheca " limited by a cuticle of chitinous 

 or other organic substance. In certain cases this is so conspicuous 

 that the generic or specific name has been taken from it (e.g., 

 Calymmophora, Lepralia vestita). The formation of layers of 

 superposed zooecia in Cellepora, etc. appears to take place as the 

 result of the separation of the epitheca from the calcareous 

 wall, the subjacent space developing into a new zooecium. The 

 secondary thickening which the calcareous front wall commonly 

 undergoes, and the occlusion of the orifices of the zooecia in the 

 older parts of the colony, in certain cases, are probably due to 

 the existence of this living membrane external to the calcareous 

 matter. The membrane usually passes into the " raised lines " 

 which may form the outlines of the zooecia. In Euthyris obtecta 

 this connexion seems to have been lost, and there is a large, 

 continuous, extra-zooecial space on the front and back walls of 

 the frond. On the front surface the space is traversed by the 

 necks of the flask-shaped zooecia, the orifices lying in the same 

 plane as the epitheca. The arrangement closely resembles that 

 described by D'Orbigny in one of the Cretaceous family Stegino- 

 poridae 1 , but if Jullien is correct in his statements' 2 , these forms 

 have developed what may be described as a tertiary front wall 

 by the growth of certain branched peristomial spines. It is a 

 noteworthy fact that the cavity beneath this tertiary wall has a 

 floor which resembles the outer surface of a Cribrilina. 



The continuous epitheca of Euthyris obtecta is held at a 

 distance from the zooecia by papillae which are calcareous at 



1 Disteginopora (Thoracophora) horrida, "Pal. Franchise," "Terrains Cr^taces," 

 v. 1850—51, p. 237, PL 687 bis, fig. 4. 



2 "Les Costulidees, nouvelle Famille de Bryozoaires," Bull. Soc. Zool. France, 

 xi. 1886, p. 609. 



