32 F. D. Longe— Oolitic PoJyzoa. 



of a long oval shape when young, and they become oblong in the 

 older or lower parts of the lamella3 through the compression of 

 ccenoecic growth ^ Hincks describes the cells in this form, which he 

 calls Leinalia foliacea, as " ovate-elongate or rhomboid," and he 

 further says : " The zooecia are liable to some variation in form, and 

 are often much elongated and sub-quadrangular." The similarity of 

 cell form in some of the Escharoid Diastoporidee of the Oolites to 

 that of Eschara foliacea is very striking.^ 



Among the various modifications which distinguish the so-called 

 Chcilostomnta from the Cyclostomata is the increased use of organic 

 material, of a membranous or horny consistency, in the comj)osition 

 and structure of the coenoecium. Modification in this direction is 

 exhibited in some species by the avicularia and vibracula, which 

 would appear to be developed from the opercula themselves by a 

 process of adaptation.^ That the opercula of the recognized Cheilo- 

 stomatous forms should be of a purely membranous or horny con- 

 stituency, while the opercula of the more calcareous coenoecia of the 

 Cyclostomata should be of a membrano-calcareous composition, 

 capable of being preserved in fossil remains, would be quite in 

 accordance with this change of character in the composition of the 

 coenoecium. It would appear that even in some of the Oolitic forms, 

 where the shape of the tubular cell was modified so as to present an 

 expanded oral extremity, the membrano-calcareous integument de- 

 veloped to cover the orifice was not all movable as an operculum, 

 but a small oral aperture was formed in the centre,* while the rest 

 of the integument became an integral part of the cell walls. 



If the view here suggested as to the connexion between the 

 Cheilostomatous and Cyclostomatous cell features is correct, there 

 can be no difiiculty in determining the true morphological and 

 genealogical position of the Oolitic Escharoids. Jules Haime was 

 right in assigning the whole group to the same genus as Diastopora. 

 D'Orbigny was right in asserting the existence of opercula in some 

 of these forms. Michelin was right in asserting the affinity of 

 some of them to the Cheilostomatous Eschara. These ambiguous 

 Escharoid forms, as represented in the Oolites, are to be regarded as 

 exhibiting complete evidence of the transformation of the simple 

 tubular cell of the older forms into the variegated cell forms of the 

 Cheilostomata, and of the close afiinity between a number of families 

 which has since been obscured by divergent development. 



If such views are correct, it will follow that the system of 

 classification which is based on the supposed absence of opercula in 

 a primary division of the whole class must be abandoned, and the 

 classification so modified as to recognize the afiinity of several 

 families now classed as members of distinct orders. 



The following is submitted merely as a suggestive sketch of the 

 genealogical arrangement of certain families which this view would 

 authorize : — 



1 See Fig. 7. '^ Compare Figs. 2, 3, 7. 



3 Hiucks, Britisli Marine Polyzoa, Introduction, p. Ixvii. * See Fig. 6. 



