NORTH AMERICAN EARLY TERTIARY BRYOZOA. 551 



snc. in which the embryo is developed. The septules are numerous, placed in linear 

 rows, arranged to correspond to the areolae. The avicularia are frontal or inter- 

 zooecial : the latter have no pivot. 13-16 tentacles. 



History. The history of this group has been given by Gregory * in some detail. 

 Primarily the name of Adeona Lamouroux, 1816, was applied to species which had 

 a fenestrated zoarium provided with radicular fibers. It was created simply for 

 a form of zoarial growth and it should never have changed in meaning. In 1884 

 Busk created the family and characterized it by the trimorphic zooecia and the 

 presence of an ascopore. In 1907 Cami discovered in the French Lutetian a group 

 of species devoid of ascopores, and formed for them the family Meniscoporidae. In 

 1909 Levinsen confirmed the fact that Bracebridgia was indeed a member of the 

 Adeonidae. whence Canu's family Meniscoporidae became superfluous. The family 

 Adeonidae is now well established on ovarian characters and important anatomical 

 features. 



Structure and terminology. It is always easy to recognize a species of the 

 Adeonidae by rubbing away one face of the zoarium so as to reveal the areolar 

 cavities of the walls (parietal areolae). This character is a general one and 

 has no exception. In all the other families of the sub-order Ascophora, the 

 areolar pores communicate directly with the interior itself of the zooecium. but 

 in the Adeonidae the areolar cavities do so by means of the septules. These cavities 

 serve for the passage and protection of the endocystal elements which must secrete 

 and deposit the pleurocyst. 



The gonoecia are often larger than the other zooecia ; their aperture is dif- 

 ferent and their frontal pores are more numerous. They develop first a normal 

 polypide, which soon disappears by histolysis and is replaced by a small polypide 

 placed at the distal extremity and a large ovicell sac occupying the greater part of 

 the gonoecium ; here the embryo is developed. The form of the gonoecia is rather 

 variable, as noted by Canu, 2 who has made a special study of this subject. 



The great thickness of the pleurocyst causes the formation of a peristomie, at 

 the bottom of which is the aperture (primary orifice of Hincks) closed by the 

 operculum and of which the form is constant. The external orifice of this peri- 

 stomie is the peristomice (secondary orifice of Hincks) ; its form is irregular and 

 it is surrounded by a more or less salient peristome. The form of the aperture is 

 often hidden, and in order to discover it, it is necessary to rub away the posterior 

 face of the zoarium to examine the interior of the zooecia. 



The hydrostatic system is quite variable. We have found all the variations 

 noted in the other families of Ascophora. The genera, which are without frontal 

 ascopores, have an operculum like Schisoporella, Hippoporina, etc., of which the 

 anterior part serves to close or to open its compensatrix. The operculum of the genera 

 provided with frontal ascopores is semilunar and water penetrates into the com- 

 pensatrix by means of the ascopores. Finally, as in Galeopsis, the water passes 

 firet into the vestibule by a spiramen before penetrating into the compensatrix. 



'British Palaeogene Bryozoa, Transactions Zoological Society, London, vol. J3, 1893, p. 241. 

 - Bryozoa Environs Paris, Annales de Paleoutologie. 1907, p. 411. 



