KETEPORA. 



rium ; but it now seems more than doubtful whether this 

 character alone can supply the basis for a generic group. 

 The reticulation is merely a peculiar form of ramification, 

 and is probably entitled to no more systematic Aveight, 

 apart from the characters of the zooecium, than the sim- 

 ple branching, which was the distinction of the old genus 

 Eschar a. The retiform zoarium is associated with very 

 different types of cell, whilst, on the other hand, a form 

 in my possession (probably from the Red Sea), which 

 cannot be distinguished generically, in other respects, 

 from many of the Retepora, exhibits no trace whatever 

 of reticulation, but has its zoarium as simply branched 

 dichotomously as an Eschar a or Hemeschara of authors. 

 Strongly marked as is the facies which its peculiar habit 

 of growth gives to the Retepore, we must not assign too 

 much weight to it as a clue to natural affinity. There 

 are some points, however, connected with the Reteporine 

 group, which may possibly have a greater significance. 

 In all cases, I believe, the zoarium originates in an ex- 

 panded crust, composed in great part of aborted cells, 

 destitute of an oral aperture, but frequently furnished 

 with an avicularium, occupying its place. The centre of 

 the incrusting base, however, is occupied by a subcircular 

 group of fully developed zooecia, round the edge of which 

 gemmation takes place at intervals in an upward direction, 

 and a number of erect lobes are thus formed, which con- 

 stitute the rudiments of the (usually) reticulate and cup- 

 shaped zoarium. (See page 394, woodcut, fig. 18.) This 

 mode of growth is very peculiar, and, so far as I know, it 

 is universal amongst the forms which have been hitherto 

 included in the genus Retepora. 



Our two British species exhibit the same type of zoce- 

 cium, and this allies them to the Escharida; I have 

 therefore ranked them in this family under the old name, 



