GENERA OF FA VOSITIDJE. 79 



remote, and in general complete. P. cristata, E. and H., how- 

 ever, sometimes exhibits structures which may possibly be 

 incomplete tabulae. Septa are usually recognisable, as minute 

 tubercles or spines, but may be wholly obsolete. Lastly, the 

 mural pores differ from those of the typical forms of Favosites 

 in being comparatively few in number, apparently arranged in 

 no regular series, and usually of large size. 



From Favosites proper, Pachypora is to be distinguished 

 principally by the thickening of the walls of the corallites, the 

 characters of the mural pores and tabulae, just alluded to, 

 affording secondary points of difference. From Alveolites, as 

 I shall here define it, the genus must likewise be separated 

 chiefly by its incrassated walls. Striatopora, Hall, is very 

 nearly allied to Pachypora, but may be separated by the fact 

 that the cup of the calice is constricted at its base, and the 

 walls below this point are excessively thickened. Trachypora 

 E. and H., is another allied type ; but in it the thickening of 

 the walls of the corallites attains its maximum, and tabulae are 

 greatly reduced or wanting. 



The only other point which need be noticed is the relation 

 between Pachypora, Lindst., and Cladopora, Hall. The latter 

 genus was originally founded by Hall (Pal. N.Y., vol. ii. p. 

 137), for branching or reticulate corals from the Niagara 

 Group, " composed of a series of tubes or cells radiating 

 equally on all sides from the axis, and opening upon the 

 surface in rounded or subangular expanded mouths." The 

 corallites are stated to be more or less closely arranged, but 

 not always contiguous, and both tabulae and septa are said to 

 be apparently absent. On the other hand, in the latest defini- 

 tion of Cladopora, Hall, as given by Rominger (Foss. Cor. of 

 Michigan, p. 45), the genus is placed among the Favositidcz, 

 and is stated to possess mural pores, with " occasionally " 

 tabulae. There can, further, be no doubt but that the Corals 

 placed by Dr Rominger under this head are in great part 

 referable to Pachypora, Lindst. ; and as Cladopora, Hall, is of 

 course a much older name, it might seem proper to suppress 



