26 F. D. Longe—OoUtie PoJyzoa. 



preserved forms, Haime's explanation is valueless. Nor can it be 

 supposed that such an observer as D'Orbigny would have gone the 

 length of establishing a distinct group, embracing several foliaceous 

 and dendroid forms, common to the Oolites and the Chalk, if he had 

 not strong evidence of the presence of opercula in the cells as well as 

 of their tubular forms. The difference of opinion among these 

 authorities as to the character of many of these forms is undoubtedly 

 to be attributed to the important fact that most of them exhibit a 

 very different character of cell feature in different pai'ts, even of the 

 same lamella. The Escharoid forms of the Oolites may be divided 

 into three groups. In one group, the cell structure is very irregular, 

 some of the cells are immersed, with their orifices immediately on 

 the surface of the lamella ; other cells close by are protruding.^ 

 In another group the protruding cells disappear, but the immersed 

 cells are irregular in length and form, and irregularly arranged.^ It 

 is in lamellae of this character that I have observed the lids which 

 D'Orbigny regarded as opercula in such a state of preservation as to 

 show that they possess the same punctured texture as the surround- 

 ing coenoecium. Such evidence, if it does not prove these lids to be 

 opercula, disposes satisfactorily of the suggestion that they are the 

 effects of decay, or the mere filling up of the cells by crystallization.^ 



In the third group, the cells are more uniform, and so regularly 

 arranged as to produce the quincunxial s^'mmetry and angular areola- 

 tion so characteristic of the Cheilostomatous EscJiaridce of the Chalk. 

 These forms are represented by the Eschara HanvilUana of Michelin,* 

 and other varieties. No unprejudiced observer can doubt the Cheilo- 

 stomatous character of this form. Jules Haime, however, was 

 compelled by his principle of classification to deny it such attributes, 

 and accordingly gets over the difficulty by identifying it with another 

 form, which he called Diastopora lamellosa, a form in which the 

 Cheilostomatous character was much less shown. 



If we refer to Hagenow's account of the Polyzoa of the German 

 Cretaceous beds,® we find that while recognizing the existence in these 

 deposits of the Escharoid forms which Milne-Edwards had classed as 

 BiastoporidcB, he does not figure or describe any specimens himself. 

 The only figure of a Diastopora of any kind which he gives is a 

 creeping form of the common type. This figure appears in a plate 

 containing Urceolate or Cheilostomatous forms, and he states that he 

 had originally classed this Cretaceous Diastopora as an Urceolate, 

 but that he had transferred it to the Tuhilipora, on the authoiity of 

 Milne-Edwards that Diastopora has no operculum. As he took no 

 further notice of the Escharoid Diastoporidce, he avoided discussing 

 D'Orbigny's view as to the operculum. The only Escharoid forms 

 which he himself describes are entered in his list as Escharidce in his 



1 See Fig 1, Plate II. Also plates to Jules Haime's memoir, and in Michelin's and 

 D'Orbigny's works above cited, il\ustra.ting Diastopora, Bidiasiopora and Mesente^i- 

 pora. 2 gee Figs. 2 and 3. 



2 Lids similarly punctured are visible in tlie non-protrudent cells of other kinds 

 of Oolitic Polyzoa when well preserved. * See Fig. 4. 



5 Die Bryozoen der Maastrichter Kreidebildung. 



