Geological Society. 231 



The corallum in this genus, as also in Fliillipmstrcea and in 

 Orionastroea, represents a stage in colonial development in which 

 the epitheca of the individual corallites has entirely disappeared, 

 and these are consequently united by their dissepimental tissue — 

 a type of colony to which the term ' Astneiform ' may be applied. 



Diagnoses. 



Aulina rotiformis. — The corallum is massive, and the corallites 

 are united by their extrathecal tissue ; all the septa dilate at the 

 theea, and those of the major cycle again dilate at their axial edges, 

 in such a luanner as to fuse together, and so build a cylindrical wall 

 or tube witliin the theca. The structure of the form is in most 

 respects similar to that of Pliillipsasfrcva, but it appears to carry 

 forward the septal characters peculiar to that genus to a further 

 stage of development. 



PhiUijysastreea. — -The corallum is composite and massive; the 

 corallites are united by their dissepiments, or are only separated by 

 a thin epitheca ; in the former case, the septa are often confluent. 

 Major and minor septa dilate at the theea ; the latter terminate 

 there, and the major septa attenuate and advance into the intra- 

 thecal region, and there often dilate again at the axial edge. The 

 central part of the corallite is occupied solely by tabulte. 



Orionastrcea. — The characters of this genus are essentially those 

 of Litliostrotion, but of a modiHed form. The corallum is compo- 

 site and massive, and the corallites are either defined by a thin 

 epitheca, or, in the more typical instances, by no epitheca at all ; in 

 this latter case the corallites are united by their dissepiments and 

 the septa are confluent. 



The distinguishing characters of the three species recognized and 

 described are as follows : — 



(1) 0. ensifer (Edwards & Haime). Septa not confluent. Cohimella present. 



(2) 0. philli'psi (McCoy) Septa confluent. Columella present. 



(3) 0. placenta (MoCoy) Septa confluent. Columella absent. 



iS'ovember 22ad, 1016.— Dr. Alfred Harker, F.R.S., President, 

 in the Chair. 



The following communication was I'ead: — 



' Characese from the Lower Headon Beds.' By Clement Eeid, 

 F.R.S., F.L.S., F.G.S., and James Groves, F.L.S.^ 



The investigations here recorded have been made at Hordle Cliffs 

 (Hampshire), where the strata, below the superficial gravel, belong 



