564 Reviews — Nicholson' 's Tabulate Corals. 



be abandoned, and that tbe only difference between tbis genus and 

 Favosites is in tbe possession, in Alveolites, of oblique calices, and tbe 

 compressed or triangular forms of tbe corallites. 



Tbe genus Pleurodictyum, Goldf., formed for tbe peculiar fossil P. 

 problematicum, Golclf., so long a puzzle to palaeontologists, is still 

 retained as distinct from Michelinia. In a form belonging to tbe 

 same genus from tbe Devonian of Nortb America, Dr. Nicholson bas 

 detected tbe presence of tbe peculiar vermiform tube wbicb appears 

 to be constantly associated with P. problematicum, but be is unable to 

 tbrow any fresh ligbt on its probable character. 



The genus Stenopora, Lonsdale, is shown to belong to the Favosi- 

 tidae, and to possess very distinctly marked characters, in the coral- 

 lites being annulated by periodical ring-shaped thickenings. The 

 position of the genus Boemeria, E. and H., is regarded as uncertain, 

 as it has not been proved to possess mural pores ; Syringolites, 

 Hinde, appears to form a connecting link between the Favositidae 

 and the Syringoporidas, and Nyctopora, Nicholson, seems to be inter- 

 mediate between tbe Favositidaa and the Columnariadas, as it possesses 

 all the characteristics of this latter family except in having mural 

 pores. 



We pass now to the next family of the Column ariadae, which has 

 been constituted by the author to include a small group, principally 

 of American Silurian corals, distinguished by the non-perforate walls 

 of the corallites, well-marked tabulae, and well- developed septa. Tbe 

 family seems to be closely allied to the Kugosa, whilst it has also 

 resemblances to the Astraeidae of the Zoantharia Aporosa. With 

 the genus Columnaria, Goldf. (= Favistella, Hall), is also associated, 

 to form this family, the genus Lyopora, Nicb. and Eth. jun. 



The family Syringoporidas is looked upon as an aberrant group of 

 the Zoantharia Perforata, having genuine but distinct relations with 

 tbe Favositidaa. The author regards the hollow processes connecting 

 the corallites, which distinguish tbis family, as homologues of the 

 mural pores of Favosites, corresponding with the hollow transverse 

 floors connecting tbe corallites in Chonostegites Clappi, Edw. and 

 H. ; whilst in the central tube of another Favosite genus, Syringolites, 

 Hinde, there is a close similarity to the infundibular tabulae of 

 Syringopora. 



Our present knowledge of the family Auloporidaa is insufficient to 

 determine its true relationship, though the author conjectures tbat it 

 may be a peculiar group of Alcyonaria. It includes the genera 

 Aulopora, Goldf., Cladochonus, M'Coy (= Pyrgia, Edw. and H.), and 

 Monilopora, Nich. and Eth. jun. 



The family of the Halysitidas is formed for the single well-known 

 genus Halysites, Fischer, and regarded as a distinct and ancient 

 group of the Alcyonaria. Halysites catenularia, Linn., is shown to 

 possess intermediate smaller tubes, indicating the existence of two 

 classes of zooids, as in Heliopora ; but in the otherwise closely re- 

 sembling H. Eschar oides, Lam., there are only uniform corallites, 

 in which, however, spiniform septa are constantly present and 

 disposed in cycles of twelve. If these septa bear any relation to 



