PORIFERA OF THE L.M.B.C. DISTRICT. 43 
Seiriola,* n. gen. 
Characterized by the tylostyles of the ectosome. This 
genus is formed for the single new species 
Seiriola, compacta, n. sp. (Pl. VIL., figs. 1 to 3). 
This sponge was found by Mr. Rutherford, Curator of 
the Biological Station, Puffin Island, in June, 1888, in one 
of the caves on the N.W. side of the island which are 
exposed only at low spring tides. 
The specimen forms a knob-like mass, lke that of so 
many tetractinellid sponges, and measures horizontally 
4cm. by 1°5 cm., and vertically 1°3 cm. It is dark grey 
in colour and has a somewhat rough surface. A vertical 
section through this sponge shows that the cortex 
(which in this species is quite identical with the 
ectosome) is extraordinarily well marked off from the 
choanosome, and further examination shows that the 
ectosome 1s both in regard to skeleton and to histological 
structure, very different from the choanosome. The 
spicules of the ectosome are tylostyles, and their shape 
and arrangement reminded me at once of Polymastia mam- 
millaris, which sponge, of course, belongs to quite a 
different group. These tylostyles measure from 0'1 to 
0°38 mim. by 0°003 to 0°006 mm. They are arranged in 
bundles, and project for about one-half of their length 
through the ectoderm (see fig. 1, Pl. VII.). 
The skeleton of the choanosome consists of megasclera 
and microsclera. The former show the following forms: 
dichotrizna, orthotriwna, oxea, styli, strongyla, tylota. 
The dichotriena are very numerous, and are arranged 
immediately beneath the ectosome, with their cladomes 
directed towards the ectosome. The rhabdome measures 
from 0°36 to 0°42 mm., the protocladus from 0°06 to 0°09 
* From Seiriol, an early Welsh saint, who is said to have had his cell on 
Puffin Island. . 
