Zoopuyva. | LOWER PALAXOZOIC RADIATA. 41 
diameter of five or six lines) ; average length nine lines, of which the three lines nearest the apex are filled with 
solid caleareous deposit ; width seven lines; casts regularly conic, subtruncate at small end, length and width 
about equal, regularly suleated by twenty-seven to twenty-eight strong, straight, primary lamellar sulci, extend- 
ing to the centre, where they are irregularly complicated into a large cellular mass ; between the larger slits are 
an equal number of finer ones, extending about three-fourths the length of the cast from the wide edge of the 
cup (representing the secondary lamella) which extend only a short way towards the centre. 
Var. a. CRENULATA (J/Coy). 
This beautiful variety differs from the ordinary type in the primary and secondary lamellar sulci, parti- 
cularly towards the edge of the cup, being bent into numerous small, angular, zigzag, flexures (perhaps from 
alternating projections on their sides). 
I might have supposed this to have been a small form of the P. elongata (Phill. Sp.) if it was not for his 
reference to Lonsdale’s figure, Sil. Syst. t. 16. 4is f. 6, which represents a perfectly distinct species which 
I have seen; the lamellz of the present species are also fewer, the size smaller, the form more regular, and 
the lamellar ridges never pitted. On the cast the lamellar sulci are regularly alternate in size, except at the 
strong simple odd lamella, on each side of which are two or three short ones. 
Position and Locality—Very abundant in the fine greenish Caradoc sandstone of Mulock quarry, Dal- 
quorhan, Ayrshire; in the schists of Cyrn y Brain W. of Wrexham, Denbighshire; greenish schists of 
Llansantfraid, Glyn Ceiriog, Denbighshire. 
Explanation of Figures—Plate 1. B. fig. 26. Natural size from the Caradoc sandstone of Dalquorhan, 
shewing the cast of the cup above, and a rough vertical section of the dense deposit of sclerenchyme which fills 
the base and lines the wall. Fig. 26a. Two of the interlamellar projections magnified two diameters, shewing 
the slits of the primary and secondary lamella. Fig. 264, Do. Two of the interlamellar projections of the var. 
crenulata. 
PETRAIA UNISERIALIS (M°Coy). PI. 1. B. fig. 25. 
Ref—M Coy, Ann. Nat. Hist. 2nd Series, Vol. VI. p. 280. 
Sp. Ch.—Corallum rapidly and regularly expanding, oblique, averaging five lines in height and width ; 
radiated with about forty-five or fifty lamellar sulci; average internal casts nearly five lines wide and two lines 
high, radiated by the deep slits of twenty-five strong primary lamellze (six or seven in three lines at the margin) 
extending to the centre where they are united and irregularly complicated ; between each pair of these slits is 
a row of numerous small close, irregular pits (representing papillze of the secondary lamellz) about three in a 
space equalling the distance of the lamellar slits apart. 
I frequently find this common species confounded with the P. bina (Lonsd.) which in form and size it 
resembles, but from which it differs completely in the primary lamellz, being simple plates, extending to the 
complicated centre, leaving deep slits in the cast, which therefore has but one set of rows of pits instead of two ; 
while in P. bina these lamelle are replaced by a row of large papillze, leaving a row of large pits in the cast, 
extending but a little way towards the centre. The secondary row of lamellar papillee (and pits on the cast 
between the slits) is much smaller, closer, and less regular in the present species than in the P. bina. Some of 
the casts present a depression in the smaller end, into which a process of the solid part of the apex must 
have penetrated. Between the lamellar sulci in some damaged specimens, obscure traces of cells seem 
doubtfully visible under the lens; if these should prove to be vesicular plates, the species should be placed 
in the genus Strephodes, thus removing it still farther from P. bina in which there is nothing of the kind. 
Var. a. Graciuis (AZ ‘Coy). 
Certain casts a little larger and of a much more elongated form than the above,—being about as high 
as wide, and having about thirty to thirty-six primary lamellar slits at a diameter of six or seven lines, 
and an equal number of rows of close small puncta, require separate mention, though I do not see that 
they differ in other respects. 
G 
