790 G. R. VINE ON POLYZOA (BRYOZOA) FUUND IN 
species (1882), I was not acquainted with the Jurassic Jdmonea 
triquetra, Lamx. In these Richmond washings, and also in Mr. 
Moore’s collection, fragments are present, though not common. 
Before, however, I pass on to describe the Richmond form, it may 
be well to make a few remarks upon the genus. 
I have not been able to refer to Lamouroux, Exposition Méthodique, 
1821, in which this genus is described ; I will therefore accept the de- 
scription given by Mr. Busk, Crag Polyzoa, p.104. In this diagnosis 
Mr. Busk says—‘ Mouths of cells disposed in parallel, transverse, or 
oblique, usually alternate, rows on each side of the front of the 
branches, which is angular or carinate in the middle.” There can 
be no objection to this description of a well-marked type of struc- 
ture. When, however, we compare the Jurassic J. traquetra with 
some of the more tubular Jdmonee of the Cretaceous epoch, a very 
marked difference is observable ; and it is because of these pecu- 
liarities that I wish, now that I have the opportunity, to direct special 
attention to Jurassic forms. 
In Miss E. C. Jelly’s collection from the Inferior Oolite (no locality — 
given) there is an adherent specimen, having all the characters of 
Idmonea as given by Busk (and presumably by Lamouroux), except 
that it is “ adherent ” instead of ‘“‘ramose.” I believe that if students 
would direct their attention to specimens of this Inferior-Oolite 
form, it would be found that from the decumbent branches upright 
ramose branches are formed. However this may be, it seems to be 
a fair conjecture that from this Inferior-Oolite species the Rich- 
mond form is developed. The peculiar character of the cell is not. 
unique on branches of this species, for in some of the Entalophore, 
from both the Inferior Oolite and the Great Oolite, a similar form of 
cell is found. I have no desire under present cireumstances to 
speculate as to the origin of distinct groups, otherwise than to 
remark upon the apparently characteristic “facies” of species of 
Polyzoa from the various horizons of the Jurassic rocks. In this 
paper I have been careful in describing the Richmond series for this 
special purpose. 
7. IpMONEA TRIQUETRA, Lamonroux. 
Idmonea triquetra, Lamx. Expos. Méth. p. 80, 1821 (Busk). 
Zoarium (decumbent?) or ramose; branches triangular, having 
an inferior side (back) rather broad and free from cells, and two 
other sides which rise from the inferior, forming an apparently, rather 
than really, carinated front. Zoecia forming obliquely linear or 
transverse rows; mouth circular; peristome thick and slghtly 
protruded ; tubes densely punctate. Owcia formed by the clustering 
of certain cells, over some of which there is a closure-lke operculum. 
Richmond series, Prof. Judd, slides 6a, 6, ¢. C. Moore’s series — 
(Meux Brewery), slide 1/27 &c. The specimens on this slide are 
much more bulky than those in the Richmond series. 
In comparing J. fenestrata, Busk (Crag Polyzoa, p. 105), Mr. 
Busk makes certain remarks which seemed sufficient to guide him 
in the separation of his species from the Jurassic J. triquetra. 
