CLASS I 



BEYOZOA 



317 



Tliis is distinguished from the remaining subclass, Phylactolaemata AUman (which 

 includes tlie freshwater forms), by the complete abortion of tlie foot, and ]jy the 

 cii'ciüar arrangement of tlie tentacles. 



The Mesozoic and Recent marine Gymnolaeniata are almost universally divided 

 into the three Orders proposed by Busk : the Cyclostomata, Cheüostomata and Cteno- 

 stomata. To these Vine has added a fourth, the Cryptostomata, and Ulrich a fifth, 

 the Trepostomata ; both of which serve mainly for the reception of Paleozoic forms. 



The detailed Classification of the Mesozoic and Cenozoic Bryozoa, especially of the 

 Cheilostomata, is less settled than that of the ancient types. This nonconformity is 

 due in part to the widely different views prevailing among authors as to the relative 

 value of the various characters upon which the groups are founded ; and partly 

 because the mode of growth and zoarial characters in general are much less constant, 

 and, therefore, less reliable than is the case among Paleozoic representatives of the 

 group. 



Subclass 1. GYMNOLAEMATA AUman. 

 Order 1. CTENOSTOMATA Busk. 



Zoüßcia usually isolated and developed hy hudding from the internodes of a distinct 

 tubulär stolon or stem. Orifice terminal, with an operculum of setce. Zoarium horny or 

 memhranaceous. Marsupia wanting. 



All of the known Paleozoic Ctenostomata have been described by Ulrich and Bassler in their 

 Revision of the Paleozoic Bryozoa, to which the student is referred for a discussion of these 

 peculiar fossils. Mesozoic and Cenozoic Ctenostomatous Bryozoa are apparently rare and little 

 study has been put upon tliem. In the Recent seas, the order Ctenostomata is specifically the 

 least represented group of Bryozoa, although some of the species are quite abundant and 

 widespread. 



/) ^ 

 Family 1. Rhopalonariidae 



Nickles and Bassler. 



Fusiform segments arranged 

 in a more or less pinnate 

 manner, impressed or almost 

 emhedded in the host. 



Rhopalonaria Ulr. (Fig. 

 437, G). Ordovician to Lower 

 Carboniferous. 



? Terebripora d'Orb. Ter- 

 tiary and Recent. 



Family 2. Vinellidae 

 Ulrich and Bassler. 



Creeping hase of zoarium 

 of simple or locally jointed, 

 delicate, tubulär threads ar- 



Fio. 437. 

 Allonema fusiforme (N. and E.), 6/1. 



_ _ _ B,C, Vlnella repens Ulr., 2/3 



ranged' either without order or ^^^^'""Ti-^Ki^^^^ 



^ ,. . , and B., 6/1. F, Hcteronema capiUareJJ. and B., ^/i. G, RhojKilonana 



proceeding from more or less «enuis U. and ß., 6/i(after Ulrich and Bassler). 



deßnitely marked centres. In- 

 ternodes with a Single row of pores or, in one genus, closely punctate ; zooecia unknown. 



Vinella Ulrich (Fig. 437, 5, 0). Zoarium of very slender parasitic tubulär threads 



