Prof. W. King on Pleurodictyum problematicum. 141 



herein taken of the position of Pleurodictyum in the animal 

 kingdom be correct, this fossil will necessarily represent a type, 

 which, although not known as living, is one that there is no 

 difficulty in conceiving to have existed ; since it forms exactly 

 the link that seems to be wanted to connect the true Corals with 

 the class Bryozoaria. 



Belmont near Galway, Jan. 9, 1856. 



EXPLANATION OF PLATE X. 

 Pleurodictyum problematicum. 



Fig. 1. View of basal or under surface of a cast, twice the natural size, 

 having the basal plate and nearly one-half of the cells removed 

 (the latter from the lower portion of figure). One of the extre- 

 mities or tails of the vermiform appendage is consequently ex- 

 posed, curving down among the cells to the opposite (upper or 

 adhering) surface : the other extremity also passes down to the 

 same surface, but becomes concealed among the cells. 



Fig. 2. Longitudinal section through the centre, partly restored, showing 

 casts of central (upright), submarginal (inclined) and marginal 

 (horizontal) cells ; also young cells with their pointed base 

 attached to the outer side of old ones. The appendage (of which 

 a cross section is exposed) is seen beneath one of the cells, which 

 is modified (shortened) to make room for it. The base of the 

 central cells exhibits the furrow or depression resulting from the 

 central prominence or median ridge thereon. The dark portion 

 at bottom exhibits the space originally occupied by the basal 

 plate. 



Fig. 3. Impression of the basal plate, twice the natural size, exhibiting 

 marks of the cell-bases, and the shell-valve (cast of Chonetes) to 

 which it adhered. The anastomosing Unes are rather too strongly 

 marked. 



Fig. 4 . Representation, thrice the natural size, of a portion of central area 

 of basal surface, exhibiting the appendage with one of its extre- 

 mities (the left) passing gradually down among the cells (or 

 rather up) to the opposite (upper) surface. This specimen, which 

 is different from that under fig. 1, exhibits casts of the foramina 

 at the cell-bases, where they are " long, curved, and sometimes 

 anastomosed ;" but always avoiding the appendage : it also ex- 

 hibits the depressions (produced by the central prominence or 

 median ridge), and the pricked holes (produced by the spinules 

 belonging to the adjoining obsolete costules) on casts of the cell- 

 bases (central and submarginal). 



Fig. 5. Cast of a marginal cell showing its (outer) sides and rhombic base, 

 with their punctured furrows and plain marginal sulcations (or 

 intervening costules). 



N.B. This figure ought to have been three times its size to 

 exhibit clearly all the characters belonging to the interior of the 

 cells. The spinulose costules (not present on this cell) are only 

 seen on the base of the central and submarginal cells. 



Fig. 6. Cast of a submarginal cell showing its inner sides marked with 

 casts of foramina linearly arranged. 



Fig. 7- Casts of submarginal cells exhibiting young interpolated ditto 



