354 



MOLLUSCOIDEA— BRYOZOA 



PHYLUM V 



portions nioie or less erect and very irregularly disposed. Orifice terminal, entire 

 or sinuated, with or without internal denticles ; in connection with it are usually one 



or more rostra Ijearing avicularia. Inter- 

 calated avicularia generally present also. The 

 surface of weathered specimens dotted by 

 the unequal apertures of vesicle -like cells. 

 Tertiary and Recent. 



Subclass 2. PHYLACTOLAEMATA 

 Allman. 



The Bryozoa referred to this subclass 

 are soft - bodied, and therefore cannot be 

 expected to be found fossil except under 

 unusual conditions of preservation. The 

 fresh -water Cenomanian beds of Bohemia 

 have yielded an organism in crusting a TJnio, 

 resembling the Recent genus Plmnatella. 

 Although the structure is too imperfectly preserved for certain identification, this 

 specimen (Plumatellites proMferus Fric) may Avell be a fossil rejjresentative of the 

 Ph y lactolaei uata. 



Fig. 525. 



Cellepora conglomerata Goldfuss. Oligocene ; 

 Astrupp, near Osnabriick. A, Zoarium, i/j. 

 B, Upper surface, enlarged. 



Range and Distribution of the Bryozoa. 



The class Bryozoa begins in the earliest Ordovician, and is represented con- 

 tinuously up to the present time. The older Paleozoic forms belong chiefly to two 

 oixlers — the Cyclostomata and Trej)ostomata. 



A considerable number of Cyclostomatous genera are present in the Ordovician, 

 most of them being closely related with Mesozoic and Recent types ; but throughout 

 the remainder of the Paleozoic, and in the Trias also, the order is very sparingly 

 represented (except for the Ceramoporidae and Fistulij5oridae), and in some parts quite 

 absent. In the Jura and Cretaceous, however, a remarkable increase took place, 

 hundreds of species being known from these formations. During the Tertiary their 

 strength was again materially reduced, and the living Cyclostomata barely exceed 

 100 species in number. 



The Trepostomata appear suddenly and in great variety in the Ordovician, from 

 which over 400 species are known, but entered almost immediately upon a period of 

 decline. From the Trenton and Cincinnati groups alone more species have been 

 described than from all of the later Paleozoic formations put together. There is at 

 present no evidence to show that the group siirvived later than the Paleozoic era, but 

 it is not unlikely that their descendants may be found among certain Mesozoic 

 families, such as the Ceidae, which are jirovisionally assigned to the Cyclostomata. 



The Cryptostomata are likewise confined to rocks of Paleozoic age, but, as has 

 been remarked above, may be very confidently regarded as the forerunners of the 

 Cheilostomata. True members of the latter group are first met with in the Jura, but 

 they develop rai)idly, and from the Cretaceous onward remain the dominant type. 



The Triassic and Liassic liryozoans belong chiefly to the Cerioporidae. This 

 family, together with the Diastoporidae, Fascigeridae, and other members of the 

 Cyclostomata, is abundantly rei:)resented in tlie Middle Jura of Lorraine, Southern 

 Germany, England and Normandy. Tlie Upper Jura, on the contrary, yields com- 

 I^aratively few Bryozoan fossils. 



The Cyclostomata still predominate in the NeocoAiian and Gault, but in the 



