XXV1 DESCRIPLIVE REMARKS. 
explain the terms used in describing these various elements of the 
calcareous structure, the only part preservable in a fossil state:— 
Fig. 5.—Parts of a Coral (after Forbes). Such forms as Petraia 
aquisulcata, Pl. x., fig. 2, 
although sometimes abun- 
dant,are of doubtful charae- 
ter. In the explanation to 
that Plate, p. 28, I have re- 
marked on the probability 
of this coral and others be- 
longing toCyathophyllum, 
a genus of turbinated corals 
arranged under the sub- 
order Zoantharia rugosa, 
by Protessor H. Milne Ed- 
wards and Jules Haime. 
Entirely agreeing with 
these eminent authors of 
** British Fossil Corals” 
Calice, or cup. 
a . . 
b. Columella. that the species which con- 
ene aoital stitute the genus Petrava 
oD mente, o: tubule or Turbinolopsis are merely 
4 1eca, . mils % 
9. Epitheca. internal casts of'simpletur- 
h. a. . : 
i. Genenchying, binated corals, having cha- 
J. Calycial budding. m3 0 Toft] 1 
k. Lateral and superior budding. racters undis tinguishable 
i, Lateral and inferior budding. from that of Cyathophyl- 
m. Fission. 
lum,* I propose to include 
in that genus the above-named species and others common to the 
Llandovery rocks, characteristic examples of which are figured amongst 
the fossils of that formation on Plate xiv., figs. 1, a, 8, ¢. 
The most universally distributed of the corals is Favosites, (Steno- 
pora) fibrosus, branching and hemispherical varieties of which are 
shown on Pl. x., figs. 1 a-d. It is most abundant (especially the 
branching variety) in Lower Silurian rocks, ranging through all the 
Silurian strata from the Llandeilo to the Ludlow formation ; its occur- 
rence in the Upper Llandeilo rocks of Wales being recorded in Mem. 
Geol. Surv., vol. iii., p. 258. 
Accompanying it in these Lower and Upper Silurian strata is the 
remarkable “‘ chain coral,”’ Halysites catenularius, figured amongst the 
fossils of the Wenlock rocks, Pl. xvii., figs. 8 a—d, as being most abun- 
daut in that formation. Helvolites interstinctus on the same Plate, 
fig. 1 a, b,c; and Favosites Gothlandicus, fig. 2 a, b,c; all these corals 
* Monograph of Brit. Fossil Corals, Paleontographical Society, 1850-4, pp. 226 
and 286. 
