138 ENTALOPHOBA. 



so worn that its exact affinities are not quite certain. The most 

 definite character of the form is that the apertures occur in annular 

 series. Blainville states, in his diagnosis of the genus, that the 

 zocecia are "regularly disposed," and he even includes in it 

 the well-known species S. verticillata (Goldf.). These three facts 

 show that Pustulopora, as used by Blainville, is a synonym of 

 Spiropora, instead of EntalopTiora. 



The limitation of Entalophora is a difficult task. As used by 

 "Waters it includes three different types 



1. Species in which the zocecia are long and cylindrical, and 



irregularly arranged. 



2. Species in which the zocecia are long and cylindrical, and 



arranged in regular lines. 



3. Species in which the zooecia are short and hexagonal. 



The question is whether these are all to be regarded as one 

 genus or as three. The early writers on the group kept them 

 distinct, while D'Orbigny even added many other divisions. 

 Thus, the first group was regarded as Entalophora, the second as 

 Spiropora (Cricopora), and the third as Melicertites. 



Waters ! has shown that in one part of a zoarium the peristomes 

 may be arranged in lines (as in Spiropora) and in another 

 irregularly (as in Entalophara). He therefore proposes to merge 

 the two groups. This evidence is conclusive that the distinction 

 between these two types is not absolute. But in the vast majority 

 of the fossil forms the distinction holds, except sometimes at 

 a point of bifurcation, where irregularity results from overcrowding. 

 It is therefore very convenient to retain the distinction, for to 

 merge the genera would necessitate the renaming of many species. 

 I accordingly accept Spiropora as a section of Entalophora. 



In regard to the group of species with hexagonal zocecia, it 

 is also true that we may find a few hexagonal zocecia in zoaria, 2 

 of which the majority are tubular. If we are to act on the 



1 A. "W. Waters. Fossil Cycl. Bry. Australia : Quart. Journ. Geol. Soe. vol. xl. 

 (1884), p. 680. North Ital. Bry. pt. ii. : ibid. vol. xlviii. (1892) p. 158. 



2 As e.g. in Busk's careful figure of E. regularis, MacG. (Chall. Bry. pt. ii. 

 pi. iv. fig. 2). 



