66 BULLETIN 106, UNITED STATES NATIONAL, MUSEUM. 



are attached fascia, but without any long tendon; they are more attached by a 

 short band to various parts of the base of the seta. The vibracular base is very 

 small, so that it is difficult to follow the complicated mechanism; the reason for 

 this complication is found in the seta being movable in all directions. Very 

 minute glands occur." (Waters, 1913.) 



There are two sorts of interzooecial vibracula, the symmetrical and the non- 

 symmetrical or auriculated (Fig. 14). 



Mucro. The mucro is a skeletal appendix, more or less salient and placed 

 before the apertura. Its function is not yet clearly known. It is elongated in 

 the more protected parts of the zoarium, just as the avicularia are. Moreover it 

 appears to have the same use. Calvet in 1902 had already mentioned that in Schiso- 

 porella ambita Waters. 1902, and in Emballotheca subimmcrsa, MacGillivray, 

 the suboral avicularium, is sometimes wanting and is replaced more often by a 

 mucro becoming confused with the calcareous thickenings which surround the 

 inferior border of the zooecial orifice in the somewhat aged bryozooids. We have 

 noticed the same thing in Metradolium labratulum, new species. In the Cellopores 

 the mucro of the deep zooecia, like the avicularia, sometimes projects to the level 

 of the uppermost zooecia. 



Spines. The function of the spines is still not yet known. They become 

 elongated in the protected parts of the zoarium. They do not exist on species pro- 

 vided with a long peristomie. 



Radicular fibers. The radicular fibers attach the zoaria to submarine objects. 

 They leave only small perforations on the zooecia or on the avicularia in most of 

 the articulated species. On the turbinated zoaria, in the Lunulites form of growth, 

 they emerge from special, small zooecia without polypide perforated by a single 

 pore. 



ZOOECIA. 



Form and size. The internal form of the zooecium is evidently in rapport 

 with the reciprocal arrangement of all the soft parts in the interior. Unfortu- 

 nately no zoological study has been made along this line which may be fruitful 

 from the viewpoint of classification. 



The external form is still more variable because of the intensity of calcifica- 

 tion. It is in evident rappoit with the surrounding medium and shows characters 

 of adaptation. The influence of the medium on the zooecial form has never been 

 the object of any zoological work. 



" More generally the length of the tentacles is in rapport with that of the 

 zooecia. In Aetea anguina, Eucratea lafontii, Bugularia, Cell aria fist:ilosu, 

 Cellaria salicornoides, Flustra securifrons, Microporella heckeli, Flustrelln 

 hispida, Pherusia tubulosa, Cylind.roecium dilatum and all the cyclostomes in 

 which the zooecia are at least two times longer than wide, the tentacles are them- 

 selves long and often exceed half the length of the bryozooid. This rule is never- 

 theless not absolute and allows rather numerous exceptions. In Bowerbanlcia 

 piistulosa, V esicularia spinosa, Amathia lendigera, and A. tcmiconvoluta, for 



