CELLULABINE AND OTHER POLYZOA. 333 
■gigantic (PI. 17. fig. 26), with a strongly hooked rostrum, its articular 
■condyles strong and spike-like, and the mandible triangular and pointed 
(as in the other avicularia^^, and with an incurved acuminate tip. Marginal 
avicularia wanting. Basal helerozooecia in the form o£ curved vibracula 
(fig. 27), placed in alternating pairs, the tip of the rostrum o£ each vibra- 
•culum meeting the middle of its predecessor on the opposite side of the 
branch. Rootlets as in other species. Ovicells resembling those of A. inula. 
Described from specimens in the British Museum, including Buslc's type 
(54.11.1,5.82). 
The basal heterozooecia o£ A. ruclis (PI. 17. fig. 27) are of the kind 
described by Levinsen (1909, p. 13.^)) as "curved or angularly bent 
vibracula " in A. henemunita, as noticed under that species. Levinsen founded 
the genus Caberiella on this character, not recognizing the fact that Menipea 
henemunita, Busk, is referable to Amastigia. Vibracula of this type occur 
in profusion in A. rudis, varying in size but not in form. The rostral groove, 
in which the long seta is received, is very long. The occurrence of different 
types of basal heterozooecia in Amastigia nuda and A. rudis indicates that 
these structures are in a plastic condition in the genus, assuming the form 
indiiferently of avicularia and vibracula, or being completely absent. 
In side view (PI. 19. fig. 52) the zooecia are very different from those 
of A. nuda, being larger in all their dimensions. The terminal wall is 
more vertical^ and the proximal end of the zooecium much deeper, the 
median zocecia being more completely represented on the basal wall than 
in that species, a fact with which the smaller amount of sinuosity of the 
basal wall (PI. 19. fig. 52) is associated. The lateral communication-plates, 
as in other species of Amastigia (as well as in Menipea), are two in number. 
The basal view (PI. 17. fig. 27) of a branch of A. rudis is very charac- 
teristic. The marginal zooecia occupy a disproportionate amount of this 
wall, but the others, though here reduced, are not nearly as much so as in 
A. nuda. Each zooecium is wide distally, where it meets the basal wall 
along its whole width. It becomes narrower proximally^ as shown in the 
distal zocecium of the median row; but the greater part of this region 
is excluded frona the basal surface by the union or close approximation 
■of the widened parts of the preceding zooecia of the rows on either side 
of it. The basal walls of all the zooecia except those of the marginal 
rows thus appear as a series of regularly alternating spindle-shaped figures. 
The basal vibracula, which are not drawn on the younger zooecia, are another 
very characteristic feature of the species. 
A. rudis differs from A. tiuda in the larger number of series of zooecia in 
its branches, in the smaller number of spines, in the distal lobe of the 
scutum which is usuallj^ pointed, in the character of the basal heterozooecia, 
in the gigantic frontal avicularia of the marginal rows, and in the larger 
measurements of all of its parts. 
