SUCCESSION OF GENERA OF BRYOZOA. 



495 



the lithographic slate of Bavaria, and have been named Lumbriconerites, 

 Ischyr acanthus, Meringosoma, Ctenosolex, and Eunicites, the last being 

 found also at Monte Bolca. Numerous genera have been described 

 from rocks of all ages, but many of them are of uncertain affinity, 

 such as Scolithus, Arenicola, Histioderma, Ortonia, Scolicoderma, &c., 

 which are well-known fossils of the Cambrian rocks. 



Bryozoa. Bryozoa are compound organisms, which form colonies, 

 and often encrust other organisms. They are found in the Primary 

 rocks represented by genera which for the most part are extinct. 

 Phyllopora, Polypora, Fenestella range through the period. Ptilodictya 

 and Penuiretipora are com- 

 mon to Silurian and Devo- 

 nian. Pcetniopora is De- 

 vonian, Hippotha and Sto- 

 matopora commence in the 

 Silurian, and still exist ; 

 Montwulipora ranges from 

 the Silurian to the Car- 

 boniferous. The Carbon- 

 iferous genera are Choetetes, 

 Archimedes, Ptilopora, Cos- 

 cmium, and Ichthyorhachis. 

 In the Permian is found 

 Acanthocladia. Ceriopora 

 is a Palaeozoic genus well 

 known in the Secondary 

 strata. Many genera com- 

 mence in the Jurassic epoch, 

 and still survive. Among 

 them are Diastopora, Bere- 

 nicia, Defrancia, Reptotu- 

 bigera, Spiropora, &c., while 

 Heteropora, Terelellaria, and 

 some others are common to 

 the Jurassic and Cretaceous periods. The Cretaceous types comprise 

 Hornera, Idmonea, Tubulipora, Discosparsa, Frondipora, Fasiculipora, 

 Vincidaria, Myriozoum, Cupularia, Lunulites, Retepora, Flusterella, 

 Eschara, Meinbranopora, which still survive. Nodelict, Multelia, 

 Osculipora, Truncatula, Cellulipora, and Semimultisparsa are peculiar 

 to the Chalk. Alveolaria, though characteristic of the Crag, com- 

 mences in the Chalk. Among Tertiary types which survive are 

 Cellepora, Cumulipora, and Eutalopora. Buslda is characteristic of 

 the Oligocene. 1 



Brachiopoda. Bvachiopods are symmetrical bivalve shells, which 

 are equal-sided, but usually inequivalve. In most genera the valves 

 are locked together; the larger valve is perforated by a foramen, 

 giving passage to a ligament, by which the shell is attached; and 



1 The Bryozoa of the Crag by Busk has been published by the Palaeonto- 

 graphical Society. 



Fig. 1 16. Fencstclla. Fig. 117. Monticulipora. 



