ON THE GEMUS ALVEOLITES ETC. 3G3 



masses, sometimes of great size (reaeliing occasionally a foot and 

 a half in diameter and five or six inches in height), and have been 

 derived from the Carboniferous Limestone series of Scotland. 

 The composition of these masses varies in different cases. In 

 some examples from Ecclefechau tlie corallum is composed of nu- 

 merous concentric layers, each layer being of comparatively small 

 thickness. In other examples, as in some huge masses from the 

 Carboniferous Limestone series of Dunbar, the corallites are long 

 and basaltiform, extending the whole height of the corallum. In 

 both cases the corallites may fairly be said to be erect, in the 

 same sense that this term is applied to the position of the coral- 

 lites in a similarly shaped mass of Favosites or Clicetetes ; that is 

 to say, the corallites in a hemispherical corallum are vertical in 

 the centre of the mass, and curve gently outwards as the margins 

 are approached, thus having their terminal portions always directed 

 at riglit angles to the surface upon which they open. Hence the 

 calices entirely want the obliquity which is so characteristic of 

 Alveolites sitborhicularis and its allies. A reference to the figures 

 of ^. 5epi!fo5« given by Milne-Edwards and Haime in the Mono- 

 graph of the British Corals (pi. xlv. fig. 5 h) will at once show that 

 the calices of this species, instead of being like those of Alveolites 

 siiiorhicularis, entirely resemble in this respect the calices of any 

 massive Favosites or Clicetetes. 



The calices in our specimens of A. septosa are from three to four 

 in a line, generally the former, their shape being somewhat irre- 

 gular, but on the whole five- or six-sided, or at any rate more or 

 less prismatic. In places the calices become transversely elon- 

 gated ; but they never assume the characteristic semilunar or sub- 

 triangular appearance of those of A. suborlicularis and its conge- 

 ners. The walls of the corallites are thin ; and the margins of the 

 calices, as noticed by M'Coy (• Brit. Eoss.' p. 82), are sometimes 

 tuberculated or coarsely granulated. 



After a careful examination of well-preserved specimens, both 

 on fractured surfaces and in polished sections, we have entirely 

 failed to detect any mural pores. Eor reasons previously stated, 

 we do not regard the apparent absence of pores in our specimens 

 as absolutely conclusive as to their non-existence, though we are 

 inclined to believe that the walls of the corallites are really im- 

 perforate. 



The corallites of our examples of ^. septosa are crossed by well- 

 developed complete horizontal tabulae, generally dispersed with 



