378 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



long, triangular, adjacent to the ascopore. On the edge of the seg- 

 ments there are numerous zooecia transformed into avicularia with 

 large mandible. 

 Measurements. — 



Vhp -0.07 mm. „ . \Lz =0.35-0.40 mm. 



Peristomice j ' •' Zooecia, 7 



U^—O.lOmm. Uz =0.18-0.20 mm 



Structure. — The axial zooecia are shorter; their frontal is much 

 thickened and forms the large longitudinal carina which decorates 

 the segments. The beak of the avicularium is always turned toward 

 the zoarial margin with much regularity. Only in the vicinity of the 

 ramifications there are sometimes zooecia transformed into zoarial 

 avicularia. The ascopore is closely united with the avicularium. 

 Certainly the latter is indispensable to the hydrostatic function. 



The bundle of fibers in each articulation is short and thick and 

 gives to the colonies a relative flexibility but not perfect articulation 

 as in many of the jointed bryozoa. It is remarkable also that the 

 articulation does not form at the same time a method 

 of branching, for the segments are always ramified 

 in the manner of rigid colonies. It is therefore very 

 difficult to know what special adaptation this mode 

 of articulation observed for the first time corresponds. 



FlG 144 Adeona Biology. — We have not had the fortune to find an 



articulata, new entire colony fixed to its substratum, and it is very 

 species difficult to learn the life history of this very special 



Mandible of a species. The zoarial life of the Adeonidae is quite 

 large avicularium, varied; one can observe creeping, arborescent, 

 X 85, from the edge dichotomous, and fenestrated zoaria, but the utility 

 of a semirigid colony rendered flexible by the power- 

 ful articulations escapes our comprehension. However, we can infer 

 that the formation of the median crest of the segments is a means 

 of stabilization and permanent equilibrium, while the large avicularia 

 along the edge of the segments have simply the function of assuring 

 a momentary stabilization. 



Among the fossil forms Kleidionella cristata Canu and Bassler, 

 1920, from the Jacksonian of South Carolina, presents the same 

 peculiarities. Its colony was as semirigid and formed of segments 

 more or less truncated at their extremity. 



Once more and in a very rare case we can note that the zoarial 

 form is only a character of adaptation and that perfectly identical 

 zoarial forms can be observed in very different families and even 

 from widely separated geologic epochs with many kilometers of 

 distance and with millions of years of time. 



Occurrence. — D. 5151. Sirun Island, Sulu Archipelago; 5° 24' 40" 

 N.; 120° 27' 15" E.; 24 fathoms; co. S., Sh. 

 Cotypes — Cat. No. 8173, U.S.N.M. 



