Busk— Poly zoa of the London Clay. 299 



selves has as yet been given. I have, therefore, been requested by 

 my friend Mr. Woodward to dravs^ one up ; and the specimens have 

 been kiadly placed in my hands by Mr. N. T. Wetherell -for the 

 purpose. 



Although the magnified figures are rather small, they are sufficient 

 to afford a very good idea of the structures they are intended to 

 represent. 



The species here figured are three in number, but beside these 

 there are one or tM^o more of which very minute specimens are 

 found amongst those forwarded by Mr. Wetherell ; but not La such 

 a condition as to admit of any satisfactoiy description. 



The figured species belong to the Families MEMBBANIPOBIDM 

 ESCHABIDJE, and GEMELLABIAD^, as understood by me and 

 defined in my monograph of the Crag Polyzoa.^ 



1. Fam. MEMBBANIPOBID^, Busk, Brit. Mus. Cat. p. 55. 

 1. G-en. Membranipora, Johnst. 

 M. Lacroixii ? PL XII. Fig. 1. 



Savigny. Egypt. P. 10., fig. 10. 

 Busk, B. M. Cat., p. 60, pi. 69. 

 Flustra distans, Hassall, Johnst. 



„ Peachii, Couch. 

 Conopeum reticulum, Gray. 



As I am unable to perceive any essential difference between the 

 form here represented and the existing species above referred to, I 

 feel justified, though, of course, with some doubt, in placing them 

 together. In general aspect, and mode of growth, usually on the 

 outside of a turreted shell, or of stones, the two agree very closely. 

 The only distinction I am able to draw between the Eocene and 

 recent form, as exemplified in a specimen now before me, collected 

 by the late Mr. W. Thompson, of Belfast, at Portmarnock, consists in 

 the somewhat greater thickness of the septa in the former. The two 

 agree also in the circumstance that in the septa of the more worn 

 cells there is an appearance of minute distant pores, which is quite 

 in accordance with the existence in very perfect specimens, of ex- 

 tremely delicate margiaal spines. 



It is to be remarked that the existing form is very widely distri- 

 buted, occurrmg very abundantly on our own shores, as well as in 

 the Mediterranean and at Madeira. It is curious, however, that it 

 has not occurred to me among the Crag Polyzoa. 



2. Fam. ESGHABIDjE, Busk, Brit. Mus. Cat. p. 88. 



Under this term I include all those species which have an erect, 

 rigid, compressed, foliaceous, ramose, lobate, or reticulate polyzoary, 

 composed of a single or double layer of cells. 



The genera in which the cells are disposed in a double layer are 

 Eschara and Melicerita, in which the two layers are inseparable, and 

 Bijiustra in which they are readily separated, when the posterior 

 surface of each layer exhibits a sort of ridge and furrow appearance. 



^ Palseontogxaphical Society's Monographs, 1859. 



