Reviews — Development of Alonticuliporoids. 



35 



aperture are retained by both. Their ranges are conterminous, though 

 the Trepostomes reached their maximum in the Palaeozoic, are rare in 

 Secondarjr rocks, and hardly ever found in Tertiary and Eecent times. ^ 

 The Cyclostomes, on the contrary, reached their maximum in 

 Cretaceous times and are very abundant now. Cumin gs' view is 

 that " the two orders are cognate and do not stand in linear relation 

 one to the other ". This can mean only that when a common ancestor 

 is reached, Cumings would consider it neither a Trepostome nor a 

 Cyclostome. I should rather regard it as a Cyclostome, and say that the 

 Trepostomes branched from the Cyclostome stock at a very early date. 

 In their earlier stages the Cryptostomes resemble the last two 

 orders, but there is a greater condensation of the protoecium and the 

 ancestrula — the latter appearing merely as a distal appendage of 

 the former.^ They may be, therefore, an independent offshoot of 

 the Cyclostomes, as Cumings regards them,^ or a side branch of the 

 Trepostome stock soon after these had diverged from the Cyclostomes. 

 Cryptostomes are confined to the Palaeozoic. 



Secondary. 



Cumings is inclined to regard the Cryptostomes as 'Palaeozoic 

 representatives' of the Cheilostomes,^ that is to say, presumably 

 that, with their modified apertures, the}^ fill the same bionomic role 

 alongside the Cyclostomes as do the Cheilostomes at the present day, 

 and not that the Cheilostomes are their linear descendants. The earliest 

 stages of those Cheilostomes in which these have been investigated 

 show the protoecium completely merged in the ancestrula — they 

 become identical. Except for the isolated record and figure by 

 Lamouroux * of Onychocella from the Jurassic Calcaire a Polypiers of 



^ "What are here considered as the post-Paleeozoic Trepostomes are the 

 Heteroporidffi, Cerioporidse, and their aUies. 



- Cumings, loc. cit., 1905. 



^ Cumings, op. cit., p. 76, 1904. 



* Lamouroux, Exposition Methodiqiie des genres de Vordre Polypiers, 1821, 

 p. 113. The three specimens mentioned in the British Museum Catalogue of 

 Jurassic Bryozoa, 1896, as coming from tlie Norman Calcaire a Polypiers are 

 not free from doubt ; one certainly and another probably are from the Cretaceous 

 of Maastricht. 



