THE MOIIPHOLOGY OF THI'] OHKILOSTOMATA. 8o7 



incomplete fusion of two snboral calcareous spines by which 

 the median pore has been cut off from the orifice. The 

 characteristic infundibuliform pores on either side of the 

 suture are perhaps parts of these spines. 



It may be pointed out in conclusion that the principal 

 results of this paper appear to be completely in accordance 

 Avith palfBontological evidence. In Canu's important memoir 

 on Cretaceous Cheilostomata (1900), the rarity of the 

 Cretaceous Monodermata, a group instituted by JuUien, 

 which corresponds in the main with the Escharina of other 

 authors, is pointed out (p. 458), and only three pages are 

 devoted to their consideration. Nearly all the remaining 

 species belong to the groups designated as Flustridas, 

 Onychocellidfe, Opesiulida3, and Costulida3. The Flustrid^e 

 correspond with the Flustrina of other authors. The 

 Onychocellidas are an important series, still represented by 

 the recent genus Onychocella, characterised by the great 

 development of the cryptocyst, and usually by the presence 

 of a peculiar form of vicarious avicularium known as an 

 onychocellium. The Opesiulida; include the recent Micro- 

 poridae and Steganoporellidse. The Costulida9 are equivalent 

 to the CribrilinidfB. These four groups are all represented 

 by a large number of genera and species. 



Gregory (1896, preface) states that ^'it is among the 

 Jurassic deposits that Ave have to seek the ancestors of 

 existing types of Bryozoa." His Catalogue of Jurassic 

 forms includes only two Cheilostomes, one of which is a 

 Membranipora and the other an Onychocella. 



It thus follows that the Jurassic and Cretaceous Cheilo- 

 stomes belonged, for the most part, to the Diplodermata 

 of Jullien (= Athyriata, Gregory, 1893, p. 22o). Both 

 Jullien, in a memoir (1888, 4, p. 8) published subsequently 

 to the original introduction of his term Diplodermata, and 

 Gregory include the Cribrilinidte in the sub-orders respectively 

 adopted by them. It appears to me that the Cribriliuidna 

 would be better left out of the sub-order. They do not agree 

 with Jullien's definition of the Diplodermata as forms with a 



VOL. 40, I'AKT 2. NKW SliKIKS. X 



