204 BRITISH JURASSIC SPONGES. 
10. PratycHonia Bropiet, Sollas. Plate XII, figs. 4, 4a. 
1885. Pxiarycnonta Bropret, Sollas. Proc. Royal Dublin Society, N. S., vol. iv, 
p. 443, pl. xxi, figs. 4—6. 
The only example of this species known is sessile, pouch- or fan-shaped, with 
incurved sides; it measures 55 mm. in height by 33 mm. across. Both the outer 
and inner surfaces are somewhat uneven, with slight rounded elevations and 
depressions. The ostia of the convex outer surface are subcircular, from ‘2 mm. to 
.3 mm. wide; those of the inner surface are very indistinctly shown, but according 
to Professor Sollas they range up to °4 mm. in diameter. There is no distinct 
canal system beyond that in the irregular interspaces of the skeleton. The 
spicules are slender, loosely connected together, without definite arrangement ; 
they are almost entirely replaced by calcite. 
Distribution.—Marlstone of the Middle Lias at Ilminster, Somerset. (Coll. 
Rev. P. B. Brodie.) 
11. Piarycnonia etecans, Sollas. Plate XII, figs. 2—2 b. 
18838. PLaryoHonta ELEGANS, Sollas. Quart. Journ. Geol. Soc., vol. xxxix, 
p- 547, pl. xxi, figs. 22—25. 
Cf. 1858. PrarycHonta (SPONGITES) VAGANS, Quenstedt. Der Jura, p. 679, pl. Ixxxii, 
fig. 8. 
Sponges growing in the form of irregular undulating plates, from 5 mm. to 
8 mm. in thickness, with curved and occasionally lobate margins. Surfaces uneven, 
with irregular hollows and ridges. When weathered, the upper surface exhibits 
a very fine reticulate network, with small circular or irregular pores, or ostia, 
from *5 mm. to *7 mm. in width; and a similar structure is present on the more 
uneven under-surface. 
These sponges sometimes grow directly attached by the under surface of the 
wall to other sponges, as in the example figured (Pl. XII, fig. 2), where the 
sponge is growing on the Hexactinellid Calathiscus variolatus, Sollas ; in other 
instances they have a short, blunted stem, or base, which is free. The specimens 
range from 50 mm. to 125 mm. in width. The originally siliceous skeleton has 
been replaced by calcite in all the specimens, and as a consequence the form of 
the individual spicules has been to a considerable extent obliterated, this more 
particularly happens where the branching extremities of the spicules interlock 
