354 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



and shape of such excavations serve very well for the identification 

 of many fossil species. 



All of the known Paleozoic Ctenostomata have been described by 

 Ulrich and Bassler 13 in their Revision of the Paleozoic Bryozoa, to 

 which the student is referred for a discussion of these peculiar fos- 

 sils which had formerly been regarded as trilobite eggs, sponge 

 borings, or foraminifera. Mesozoic and Cenozoic ctenostomatous 

 bryozoa are apparently rare, and little study has been put upon them. 

 In the recent seas, the order is specifically the least represented of 



tentacles— 



collar-' 



anus ' 

 esophagus' 



retractor muscles- 

 coecum**" 



funiculus"* 



-retracted tentacles 

 ••-ovary 



—•'testis 



tubular stolon-i — 



Fig. 5. — Structure of the Ctenostomata. Three polypides of Farrella 

 repens Farre, rising from a stolon, one with expanded tentacles, 

 another with tentacles retracted, and the third in the young stage, 

 highly magnified. Eastern Atlantic. (After Van Beneden.) 



the bryozoa, although some of the species are quite abundant in 

 individuals and widespread. Hincks's 11 memoir of 1880 on British 

 species and Harmer's 15 work on the East Indian forms published in 

 1915 will give the student a good idea of the recent Ctenostomata. 

 The latter publication includes a good account of the methods of 

 study necessary in this order. 



In figure 5 the anatomy of an animal of a recent ctenostomatous 

 bryozoan is illustrated, and its similarity to that in the other orders 



13 1904. Ulrich and Bassler. Revision of the Paleozoic Bryozoa. Part 1, Ctenostomata. 

 Smithsonian Misc. Coll., vol. 45, pp. 256-294. 



« 1880. Hincks. British Marine Polyzoa, pp. 488-582. 



15 1915. Harmer. Polyzoa of the Siboga Expedition, pt. 1, pp. 36-92. 



