CELLULAEINE AND OTHER POLYZOA. 329 
be wanting. The mandibles o£ the avicularia are invariably of the pointed 
type. The terminal wall o£ the zooecium is at first vertical, its origin from 
the basal wall straight or slightly curved, but then bends distally, in 
approaching the frontal surface ; the proximal portion of each zooecium thus 
overlapping its predecessor on its basal side. The ovicells are hyperstomial. 
frequently completely contained in a depression on the frontal wall of the 
zooecium which succeeds the fertile zocecium, and not projecting beyond the 
general frontal level of the zooecia. 
The scutum and the heterozocecia appear to be very capricious in their 
occurrence. In several of the genera one or more of these sti'uctures 
are present, on most of the zooecia, in certain species ; while they are absent 
in other species which appear to be closely allied to those of the first series. 
I think the only interpretation which can be given of these facts is that all 
these structures are to be regarded as original possessions of the Family, 
and that their absence is to be attributed to loss. 
Dr. W. D. Lang has come to a similar conclusion with regard to Creta- 
ceous Cribrimorphs (1922, Cat. Foss. Bry. (Pol.) Brit. Mus. iv. pp. 3, 156, 
and elsewhere). 
The extreme amount of loss is found in Irieellaria peachii, in which scutum 
and heterozocecia are completely wanting, if exception be made of the 
possibly vestigial vibraculum which has been described on p. 324. On the 
assumption that the heterozocecia are structures which give their possessors 
some advantage in the struggle for existence, it is very difficult to understand 
the frequency with which they disappear entirely ; the species in which this 
takes place continuing to exist, apparently with undiminished efficiency. 
Genera here considered : — 
1. Amastigia, Busk. 
2. Menipea, Lamouroux. 
3. Notoplites, n. gen. 
4. Tricellaria, Fleming. 
5. Emma, Gray. 
6. Scriqjocellaria, Van Beneden. 
[The genera Canda and Caberea are omitted.] 
1. Amastigia, Busk. 
Amastigia, Busk, 1852^, p. 40. 
Caberiella, Levinsen, 1909, pp. 134, 135. 
Anderssonia, Kluge, 1914, p. 617, 
Scrupocellaria (pars) and Menipea (pars), auett. 
Zoarium usually unjointed, the branches in nearly all cases pluriserial. 
Frontal surface typically convex, so that the marginal zocEcia face outwardly, 
the basal surface more or less flat, the zooecia of the median rows as a rule 
partially or completely excluded from it. Spines, scutum, frontal and 
marginal avicularia present or wanting. Basal heterozooecia typically 
