on the Genus Paleeacis. 213 
wards or laterally and sometimes obliquely, with circular 
or oval crenulate margins, not all on the same plane, sepa- 
rated from one another by shallow depressions. Base, in 
depressed forms, flat or somewhat concave ; in cuneate or tur- 
binate examples it is laterally compressed or prolonged down- 
wards in the form of a small peduncle, usually concentrically 
ridged. Parts of the skeleton between the cups, and also the 
lower surface more or less, are covered with vermicular ridges 
or granules, and are often pierced by rounded or elongated 
pores of considerable size. Interior of the cups marked with 
a variable number of granules arranged in a more or less 
radiating manner, and pierced near their upper portions by 
similar apertures to those just mentioned. Structure, to the 
naked eye, when the skeleton is fractured, spongy. Micro- 
structure, consists of a calcareous tissue, pierced, more or less 
extensively, by a system of microscopic tubuli, in parts com- 
pact, in others more or less vesicular or trabecular. 
Obs. With the aid afforded by a particularly fine collection 
of what appears to be the commonest British species, P. eyclo- 
stoma, Phill., in conjunction with the characters of the other 
published species, we have been able to extend the generic 
diagnosis of Paleacis. So far as our researches have at 
present gone, we are acquainted with at least three well- 
defined species of Paleacis in British Carboniferous rocks ; and 
it is upon the structure of these that our knowledge of the 
genus is based. 
The surface in all the species of Paleacis seems to be more 
or less granular, or covered with vermicular strie or ridges ; 
but the precise appearance varies in different cases. In P. 
cuneiformis (Pl. XII. figs. 9-12) the surface is covered with 
numerous irregularly-curved, subparallel, sometimes bifur- 
cating, vermicular ridges, placed about their own diameter 
apart. We have not satisfied ourselves that any large pores 
can be detected on the surface of examples of this species ; but 
the summits of the ridges above alluded to appear to carry 
lines of small pores, now filled with calcite, and the entire 
substance of the skeleton has a fine spongy aspect. This ap- 
pearance, however, is more noticeable in slightly rubbed spe- 
cimens. In P. obtusa the surface-characters are the same as 
in P. cunetiformis. In P. cyclostoma the surface is covered 
with innumerable granules, small tubercles, and vermicular 
ridges, which do not show the same-subparallel arrangement 
as in the two preceding species, but are disposed irregularly, 
or sometimes with a tendency to form lines. In many cases 
the surface of the skeleton between the cups is distinctly per- 
forated with large rounded or oval pores, leading into the 
