29 
mötre, dans les individus jeunes il arrive qu’elle n’ait que I et 2 
Ctm.; elle recouvre de petites pierres et des debris de coquilles en 
les enveloppant de tous cöt&es pour n’en laisser quelquefois qu’une 
petite partie & nu de sorie que seul un examen attentif nous permet 
de ne pas la considerer comme une €ponge a existence libre, non 
fixee a des objets &trangers” (l. c. pag. 4). I have no doubt 1°. 
that my Sponge is identical with that of de Merejkowsky, for the 
whole description and the illustrations agree one with another; and 
2°. that it is identical with Bowerbank’s P. mammillarıs. There is 
yet a little partieularity in the notice of Mr. de Merejkowsky, viz. 
that he identifies with his specimens the larger flat ones. „Üepen- 
dant” says he pag. 4 „le cabinet Zoologique de l’Universite de 
St. Petersbourg possede deux enormes exemplaires de pres de 12 
Ctm. de diametre provenant du Nord de la Norvege; ils ont la 
forme de plaques comparativement minces (pres de 1 Ctm. de gros- 
seur) recouvrant la surface superieur de grandes pierres’. The 
„Willem-Barents” has on the third voyage (1880) dredged up several 
ofthese great disks, which I hope to describe afterwards: and now I am 
convinced that these are identical with the specimens under description. 
I have figured two specimens of the first expedition. The grea- 
ter one measures about four Um. the smaller ones only two or two 
and a half. They are all attached with the convex side to little 
stones, or shells from Molluscs or Worms. The more flattened 
side bears the large papillae. 'This appears to be the normal shape; 
but there are specimens where the body is thicker or flatter. As 
is to be seen in a vertical section, most all tubes are hollow. 
These tubes, perfectly described by de Merejkowsky show the par- 
ticular arrangement of the bundles of spieules. I have again given 
an illustration of the tube in figure 127 on plate IV, observed at 
a low power, and in figure 128 still more magnified. The tube 
that I have chosen for my illustration is not opened above. 
The characteristic arrangement of the spicules in the body is also 
described by de Merejkowsky. I refer to his interesting paper. The 
forms of spieules I have found in the Sponge, are the following 
(Pl. IV, figg. 129— 132). 
