Mr. A. W. Waters on the 
278 ' 
on the substratum; each subcolony is slightly raised, with 
the rays elevated above the central portion. 
Loc. Upper Greensand (£tage 20 e ), Le Havre, l’ile Ma¬ 
dame. Living: Naples, brought on a stone with Gorgonia 
&c. which must have come from a depth of over 50 fathoms. 
109. Reticulipora dorsalis , nov. (PI. XXIII. figs. 5-11.) 
Reticulipora nummulitorum, Smitt, Krit. Fort. of. Sk. 1866, p. 433, 
pi. ix. D. 1, 2, pi. x. A, B,C. 
This elegant species commences as a flat disk, or Diastn- 
pora stage; soon one or more radiating projections are formed, 
which become erect foliations (fig. 8), and from which dicho- 
tomously and irregularly further foliations spring (fig. 10); 
sometimes they curve over, and several branches may point 
in the same direction (fig. 7). There are on both faces of the 
foliations series of cells, alternate ; the series of cells are usually 
very regular, but occasionally the rows can scarcely be dis¬ 
tinguished. The number of zooecia in a series diminishes to¬ 
wards the ends of the branches, which are sometimes quite 
pointed. The dorsal surface is rounded, with cells immersed, 
often with faint median ridge ; on the dorsal surface all 
the cells I have examined have a cover with projecting tubule 
(fig. 5) in the centre ; and on other cells they are very frequent. 
Similar covers are found on many of the Cyclostomata; but, 
from the constancy on such a species as the present, I doubt if 
their signification is fully understood. I have not any speci¬ 
mens which could be called reticulate, though the foliations 
occasionally join ; but in the British Museum there is one 
from Algiers, collected by J. Y. Johnson, as distinctly reticu¬ 
late as any from the chalk (see fig. 9). 
This Algerian specimen is first a wide irregular Diasto- 
pora from which a wide foliation grows. This resembles the 
fossil from the Pliocene of Bruccoli which I called Mesente- 
ripora , sp. The mode in which it develops in the perfect 
stage (fig. 9) is not shown; but, as far as I have had the op¬ 
portunity of examining this, it appears to be the same as the 
Naples species, though growing somewhat differently. 
This is closely allied to Reticulipora nummulitorum , D’Orb., 
R. papyracea , D’Orb., and Idmonea compressa , Rss. & Man- 
zoni; but the dorsal surface distinguishes it. 
The calcareous septum distinguishes it from Idmonea ; but I 
am not sure that it should not be united to Mesenteripora. At 
one time I thought it was a variety of M. meandrina; but this 
was upon insufficient grounds. 
Fig. 6 is the end a of fig. 7, more magnified. Fig. 11 
shows a transverse section. 
