92 TABULATE CORALS. 



space of two lines, measured transversely as regards the axis 

 of the frond. Calicine margins much thickened. Septa ob- 

 solete ; tabulae few, remote, and complete. Mural pores few, 

 large-sized, irregularly distributed. 



Obs. — The above diagnosis gives all the principal characters 

 of this species. Originally described by Mr Billings, and 

 subsequently by myself, as an Alveolites, it was referred by Dr 

 Rominger to Hall's genus Cladopora. I have, however, already 

 given my reasons for thinking that this generic name cannot 

 be advantageously retained ; and the present form, at any rate, 

 differs from those to which Professor Hall originally gave this 

 title, in the possession of well-developed tabulae. At a still later 

 date it was referred by Mr R. Etheridge, jun., and myself to 

 Pachypoi'ay Lindst. ; and its very close alliance with P. lamellicor- 

 7iis, Lindst, renders the propriety of this reference undeniable. 

 The specific differences between these two forms are, however, 

 numerous ; and though it possesses the internal structure of 

 Pachypora, the present form in external characters very nearly 

 approaches Alveolites, Lam., and thus forms a connecting-link 

 between these two generic types. The corallum in P. Fischeri^ 

 Bill. (fig. 1 6, a), is a palmate, flattened, and undulated ex- 

 pansion, which doubtless attained considerable dimensions 

 though the larger examples (three inches or more in length) 

 are always broken ; while the thickness varies from one to three 

 or four lines. At its base, the corallum was fixed to some 

 foreign body, but its entire free surface is occupied by the 

 calices, the corallites diverging regularly from an imaginary 

 plane midway between the two flat surfaces of the frond 

 (fig. 1 6, b). The corallites thus open obliquely on the surface, 

 but the apparent obliquity of the calices varies greatly. In 

 some examples (fig. i6, c) the calices are very slightly oblique, 

 oval or circular, and in these there are about three calices in 

 the space of two lines, in whatever direction the measurement 

 be taken as regards the frond. In other cases (fig. i6, d) the 

 calices are oblique, oval, or subtriangular, or lozenge-shaped, 

 sometimes with the thin lower lip characteristic of Alveolites, 



