F. I). Longe — Oolitic Polyzoa. 29 



duction, and to be equivalent to ovicells, but 1). Sarniensis is provided 

 abundantly with ooecia of the usual character, a fact which must throw 

 doubt on this interpretation."^ It is to be observed that in this 

 passage Mr. Hincks has not hesitated to adopt Smitt's term " oper- 

 culEe " as applicable to the lids which appear iu this species of 

 Diastopora. 



Mr. Hincks's description of the cells in the common form D. ohelia 

 is as follows : " Zooscia moderately' slender, minutely punctate ; surface 

 flattened, usually with only a short portion of the anterior extremity 

 free and snb-erect orifice sub-circular." - To this he adds iu his 

 further remarks on the species : " In some cases many of the cells 

 are closed at the top, but they ai'e never furnished with the tubular 

 process which occui's in D. Sarniensis." With reference to this tubular 

 process in the opercula of D. Sarniensis, Mr. Hincks has this impor- 

 tant note : "Busk mentions a minute central perforation as occurring 

 in the calcareous lid with which the cells are furnished in Mesenteri- 

 pora."^ Now it so happens that Mesenteripora, Blainville and Busk, 

 is one of the generic names given to some of these very Escharoid 

 forms, the character of which we are discussing. I shall not com- 

 plicate my argument by suggesting any theory as to the "central 

 holes," nor as to the " tubular processes." But the apparent con- 

 nexion between these features furnishes further evidence of the 

 connexion between the "' calcareous lids " of the Oolitic Escharoids 

 and the " opercula " of D. Sarniensis. 



These passages show conclusively that the coenoecia of the Diasto- 

 poridce contain cells closed with lids of some kind, while they suggest 

 no better ground for distinguishing them from the opercula of the 

 Cheilostomata, than Jules Haime did for rejecting D'Orbigny's view 

 as to the opercula of the Eleidce. The only grounds which appear 

 to have been suggested are that the cells in which they are seen are 

 different from the cells occupied by the living zoids ; or that the lids 

 themselves show evidence of being fixed, and so not usable as oper- 

 cula. But Mr. Hincks evidently failed to satisfy himself that the 

 cells in which they appear had any different character or function 

 from those in which they do not appear. As to the suggestion that 

 they are " doors " which did not open, the number of the closed cells 

 in many coenoecia is altogether opposed to the view that they are only 

 the fixed coverings of abortive cells. That these lids should become 

 thicker and more calcareous with age, and remain permanently fixed 

 after the absorption of the zoid, would be quite consistent with their 

 having been movable during its life. 



The shape and position of these lids in the orifices of the shell is 

 identical with that of the opercula in some of the recognized Cheilo- 

 stomatous forms. It appears from Mr. Waters' account of the opercula 

 of the Lejjralidce that the greatest variety exists in this single group 

 in the form and position of the operculum, and as to the mode in 

 which it is attached and moved. I'lie more perfect arrangement of 

 a door or shutter fitted to the outside rim of the orifice by a visible 

 hinge and muscle, is by no means universal. In some cases the 

 1 Ibid. p. 464. 2 jii^^ p. 462. 3 Bid. p. 460. 



