Dr. W. Marshall on new Siliceous Sponges. 399 
related to one another—the two are just very similarly modi- 
fied descendants of different nearly allied marine siliceous 
sponges. One of them belongs to the comparatively modern 
relict-fauna of Lake Baikal, in which it dwells together with 
a whole series of inferior marine animals, and even seals ; 
the other has wandered into the Congo, where it occurs 
together with very remarkable still undescribed bivalves of 
Chama-like habit, which adhere by one shell, and have a black 
epidermis as in the Najades. 
Uruguaya* seems to be very nearly allied to Potamolepis 
in habit, and especially to the second species, P. Pechuélit ; 
and I would have named the group after this genus, if it had 
not a name so awkwardly geographical. A direct genetic 
connexion between these West-African and South-American 
forms may certainly be regarded as out of the question, for 
the relations and similarities between the Ethiopic and Neotro- 
pical faunas, multifarious as they are, are either due to analo- 
gies, or date back to a time when direct communication 
between the Congo and the Uruguay river by means of fresh 
water will hardly have existed +. 
The other, very probably older, freshwater sponges have a 
common character in the gemmules—a character which I 
indeed, as already indicated, regard as of subordinate im- 
portance, but which, nevertheless, is serviceable for character- 
ization in an artificial system. ‘This second group again con- 
sists of two subgroups, the Parmuline and the true Spongille, 
which are remarkably distinguished from each other in their 
general habit. ‘The former are eminently rigid, and in other 
respects also, especially in the gemmules themselves, present 
important peculiarities; they are neotropical and distributed 
especially in the Amazon and its affluents. 
The second subgroup, that of the Spongille, is cireumpolar, 
Palearctic, Nearctic, Indian, and Ethiopic, with forms pushed 
forward, on the onehand, to the Amazon (Sp.navicella, Meyenia 
gregaria, and the species of the genus Zubella, Carter) ; and, 
on the other}, to the Mauritius (Sp. Carter¢), and even, which 
is very remarkable, as far as Australia (Meyenia Capewelli, 
Cart.), and consequently is nearly cosmopolitan. For these 
forms a direct genetic connexion may be possible, but not 
more probable than spontaneous formation. In the structure 
* A genus established, but only as provisional, by Carter, Ann. & Mag. 
Nat. Hist. ser. 5, vol. vii. p. 190. : 
+ See A. R. Wallace, ‘Geographical Distribution of Animals,’ vol. ii. 
p. 81. ron , : ES " 
{ See Carter’s memoir in Ann. & Mag. Nat. Hist. ser. 5, vol. vii. 
pp. 77 et seqq. 
