VINE : CAMBRIDGE GREENSAND. 
23 
18. — Membranipora Dumerilii, Aud. (Hincks Brit. Mar. Pol., 
p. 156) var. CANTABRIGENSIS n. var. PI. II., fig. 10. 
Zocecia^ small ovate, or irregular in outliue, three cells measure 
about three millimetres, occasionally rather more or rather less 
margins sloping inwards, smooth (?) or with faint indications of 
the former existence of spines. Oceciu, globose. Avieularium, large 
pointed, on one or both sides of the ovicell, and occasionally between 
other cells as well. Cells separated by interspaces. 
Locality : Cambridge, Greensand. 
I have hesitated considerabl}^ before giving the above name to 
this Greensand species, and I do so now on account of the peculiarity 
of the ovicell and the placement of the lateral avieularium. The 
form, however, is more closely related to Mr. Busk's figure of 
M. Pouilletii (Crag. Pol., Fig 6, PI. III.), than to Mr. Hincks' (Fig. 
3, PI. XX., Brit. Mar. Pol.), and it differs from both in the way in which 
the cells are separated, and the comparative scantiness of the ovicells. 
Avicularia are very freely distributed between the cells in the 
colony, but there is generally one avieularium on either side of the 
08ecium, but rather longer and more pointed than those figured 
either by Mr Busk or by Mr. Hincks. There are slight variations 
in the form of the cell but its characteristic features are similar to 
the Crag form, but not so distinguishable as the recent ; yet, even 
in this Mr. Hincks says, " There are slight diversities in the shape 
of the cell : but in its prevalent and characteristic state it is 
contracted at the top and broad below. The ovicell is often much 
produced : but it also assumes a more rounded form." 
I have compared the specimens — which are rather abundant in 
the Cambridge material — with the figures of Membranipora in the 
works of Hagenow and Novak, none of which are sufficiently 
characteristic for the placement of the present species. The nearest 
approach to the Greensand form is given by Manzoui (Castrocaro, 
PI. II., Fig. 21) as M. Flemingii^ Busk, only that the ovicells and 
avicularia are smaller ; M. Flemingii, Busk (Brit. Mus. Cat., pi. CIV., 
fig. 2) is a synonym of J/. Dumerilii (Hincks). 
