348 vine: classifications of cyclostomatous polyzoa. 
these animals, account should be taken of all the forms in the life- 
series together, and sketches an arrangement suggested by the study 
of the larvoe (p. 250), for comparison with that of Smitt, from which 
it differs in some respects." 
One of the real difficulties which the systematist has to encounter 
in dealing with Fossil forms, is shown by Mr. A. W. Waters, in his 
paper on the " Fossil Cyclostomatous Bryozoa, of Australia.'" The 
author says: "The determination of the Cyclostomata presents 
much greater difficulties, and is much more unsatisfactory than that 
of the Cheilostomata, as there are fewer characters that can be used." 
In classifying the Tertiary Cyclostomatous Bryozoa, of Australia, 
Mr. Waters endeavoured to free himself, to some extent, from the 
modes of other authors in dealing with the group, and in doing so, 
he presents to the student new lines of investigation. The size of 
the aperture, as pointed out by Smitt, and re-worked by Mr. Waters, 
seems to be fairly constant in the same species The variation in 
size is not very great, ranguig only from 0.03 millim. to 0.2 millini., 
in all species measured ; but anything greater than 0.16 millim., or 
less than 0.07 milHm., is very exceptional," (p. 675.) One of the 
more useful characters in the Cyclostomata for determining specific — 
and perhaps even generic variation — is found in the calcareous 
closure,t wdiich may be noticed in some of this Zooecia of Recent, 
Tertiary, and even Cretaceous Polyzoa. " The position of these 
closures, together with the nature of the perforations, is a character 
of considerable importance," although it is neither so available nor 
so important as the horny operculum," of the Cliilostomata (Q. J. G. 
Soc. Vol. xl., p. 675.) 
After touching upon these purely structural features of the 
Cyclostomata, Mr. Waters offers many suggestions as to the arrange- 
ments of the group, and on this head he does not differ very materially 
from that of Mr. Busk and Mr. Hi neks, except that in discussing the 
merits of some of the genera accepted by lleuss and others, he 
questions their value. These will be referred to again further on. 
* Q>iart. Joara. Geol. Sos. Vol. xl., p. 674. 
t Closure of the Cyclos. Brytzoa. Jour. Linn. Soc. Vol. xvii,, p, 400. 
