24 F. D. Longe — Oolitic Polijzoa. 



concerned at present with the creeping Diastopora. This form 

 occupies a very different position among the living Polyzoa from that 

 which it occupied in the Oolitic period. In the Oolitic beds it is 

 very abundant, and represented by a considerable number of 

 varieties ; while the creeping forms are so manifestly connected by a 

 similarity in the character and variations of their cell features with 

 some of the common Escharoid forms of the period, that Milne- 

 Edwards classed both groups together as different species of the 

 same genus Diastopora.^ Among living Polyzoa. the creeping 

 Diastopora, although common, appears to be represented by a smaller 

 number of specific varieties, while it presents little, if any, recog- 

 nizable affinity to the Eschai'oid forms of the present seas. The 

 living Escharoids appear rather to be connected with another group 

 of creeping forms, the Lepralidcs, Busk,^ which, although identical in 

 habit of growth, and often associated on the same substance of 

 attachment with Diastopora, are generally speaking distinguishable 

 from that form by a marked difference in their more characteristic 

 cell features ; a difference which has been made the basis of distinc- 

 tion between the two groups or sub-orders called the Cyclostomata 

 and the Cheilostomata. According to this division, the Diastoporida 

 belong to the Cyclostomata, and the Lepralidce to the Cheilostomata. 

 And it follows that, if this principle of classification is to be applied 

 to the Oolitic Polyzoa, the Escharoid forms of that period, which 

 Milne-Edwards determined to be Diastoporidce, must be assigned to 

 the Cyclostomata ; while the Escharoid forms of the present seas, 

 the EscharidcB, or, as Hincks designates them, the foliaceous Lepra- 

 lidce, etc.,^ are by all systematists classed with the Cheilostomata. 

 But it is clear that the Escharoid forms, whether they appear in the 

 Oolitic or any subsequent group, have a marked feature in common, 

 which, if it does not imply generic affinity, at all events distinguishes 

 them from all other calcareous forms, viz. the peculiar mode in 

 which the foliaceous lamellse, of which the coenoecia consists, are 

 formed by the growing together of two layers of cells, placed back 

 to back. 



If then, this principle of classification is sound, the similarity in the 

 structure of the coenoecium in the Escharoid forms must be regarded 

 only as a coincidence in the development of form in two distinct 

 races. And there would be no objection to such a view, if the 

 Escharoid forms, as exhibited in these different periods, presented a 

 difference in cell feature corresponding to the different characteristics 

 of the two orders. It is perfectly clear, however, that some of the 

 Oolitic Escharoids themselves possess the characteristic cell features 

 of the Cheilostomata in a marked degree ; and their affinity to the 

 Cheilostomatous Escharidce has been recognized by no less authorities 

 than D'Orbigny * and Michelin.* Assuming then that this principle 



1 I have a specimen of an Oolitic Diastopora which, after incnisting a nodule, has 

 just commenced a bilaminate upright growth. See Busk's Fossil Polyzoa of the 

 Crag, p. 109. ■^ See Fossil Polyzoa of the Crag, p. 63. 



^ British Marine Polyzoa, Lepralia foliacea, p. 301. 



* Paleontologie Fran9aise— Terraines cretaces. * Iconographie, Zoophytologique. 



