332 Rev. T. Hincks's Contributions towrirds a 



MacGillivray describes two species which he regards as 

 new, C. ligulatum and C. spicatum ; but the differences 

 between these forms and M. rohornta must be rej^arded, I 

 think, as merely varietal. The unilaminate condition of the 

 zoarium has certainly no specific value ; cases are not rare in 

 which the bilaminate structure and the unilaminate occur in 

 one and the same species. The other points relied upon — the 

 more slender branches, the occurrence of one avicularium 

 instead of two, the slight differences in the spines, and the 

 spike-like process on the ooecium — are all well within the 

 limits of specific variation *. 



Ibid. (p. 70 Sep.). 



Memhranipora amplectenSj sp. n. 



This interesting form is entitled to rank as the type of a 

 new genus on the ground of the remarkable structure of its 

 ovicelligerous cells. The ooecium itself is not merely a varia- 

 tion upon the ordinary form, but has a distinct morphological 

 character. 



Family MembraniporidaB. 



Heterocecium, gen. no v. 



Zooecia pyriform, aperture large, occupying about two thirds 

 of the front, closed in by a membranous covering and fur- 

 nished with marginal spines (calcareous) ; immediately below 

 the aperture a tall articulated spine. Oacium borne on 

 gigantic cells, which are elongate and of considerable width, 

 extending over almost the whole of the aperture, which is 

 covered by a roof composed of rib-like processes springing 

 from the o])posite sides of the cell-wall, and bending slightly 

 inward so as to meet in the centre, where their extremities 

 are soldered together, whilst they are united laterally by a 

 calcareous expansion, the oral arch pointed; ovicelligerous 

 cells placed between the divergent lines of zooecia at a bifur- 

 cation. 



This form is nearly allied, so far as the structure of the 

 zocecium is concerned, to the group of ]\lembraniporid£B which 

 Busk (following d'Orbigny) has referred to the family Elec- 

 trinidge f, but is separated from it and from all the Cheilo- 



* C. lifjulatuni nnd C. spica/ion are placed amongst the svuoiiyms of 

 Memhrauipurn rohorata in Miss Jelly's ' Catalogue.' 

 t ' rhallenger' Keport, pt. ], p. 77. 



