PORIFERA OF THE L.M.B.C. DISTRICT. 41 
0'003 mm.) standing perpendicularly to the longitudinal 
axis and projecting for half their length through the 
ectoderm. One spicule of the former kind is given in fig. 
1 a, Pl. VI.; one of the latter kind in fig. 1 6, Pl. VI. In 
regard to the arrangement of the spicules see figs. 2 and 8, 
Elev, 
Polymastia robusta, Bowerbank. 
Dredged in Church Bay, near Holyhead, on the ‘“‘ Hyzena”’ 
Expedition of 1886. The largest of the three specimens 
has a flat basal mass, 5°5 cm. by 4 cm. in horizontal 
expansion and 1°5 cm. in thickness. On one side it bears 
between 30 and 40 papille, which in the natural condition 
probably are standing upright, but now have become 
pressed down upon the basal mass. These papille are 
laterally compressed and vary greatly in size. The largest 
measure 2 cm. in height and 7 mm. in breadth. They 
taper towards the extremities, but there are no oscula 
visible on their extremities. The dermal membrane 
can very readily be torn off from the basal mass. The 
colour of the specimens, which have been kept in spirit for 
nearly three years, is whitish. The skeleton consists of 
styli, which are of two different sizes: 0°6 mm. by 0°01 mm. 
and 0-17 mm. by 0'004 mm. The arrangement of the 
spicules is similar to that of Polymastia mammillaris. 
_ According to Bowerbank, Polymastia robusta is found 
on the coast of Northumberland. 
Order IV. TETRACTINELLIDE. 
Tethya lyncurium, J. . 
Dredged in Church Bay, near Holyhead, on the ‘‘ Hyena”’ 
Expedition of 1886. This species had not previously been 
recorded in the L.M.B.C. district, although it is found, 
according to Bowerbank, at various localities on the British 
