304 Mr. H. J. Carter on Spongiophaga Pottsi. 
in the ‘ English Mechanic,’ vol. xu. p. 469, I named a very 
distinct species now in my possession C. obtusus. 
Paleontologists interested in the minute structure of Coal- 
measure fossil teeth should refer to Dr. Barkas’s papers in the 
‘Dental Review ;’ they embrace Diplodus, Hybodus, Clado- 
dus, Ctenoptychius, Petalodus, Petalodopsis, Pleurodus, Peeci- 
lodus, Helodus, Janassa, Paleoniscus, Pygopterus, Acrolepis, 
Cycloptychius, Gyrolepis, Megalichthys, Rhizodus, Rhizodop- 
sis, Strepsodus, Orthognathus, and Archichthys, and, had Dr. 
Barkas not left England for Australia, would have included 
Ctenodus, Celacanthus, Acanthodopsis, Platysomus, and 
Amphicentrum. 
XXXV.—On Spongiophaga Pottsi, n. sp. 
By H. J. Carter, F.R.S. &e. 
[Plate XVIL.] 
In the ‘Annals’ for September. last I published a short 
notice of a parasitic growth on Spongilla which Mr. Edward 
Potts of Philadelphia, United States, had sent to me, under 
the impression, very naturally, that it was a growth of the 
sponge itself; and so it may be to a certain extent, much as 
the “gall” on the oak tree is a growth of the latter around 
the egg deposited by an insect which makes use of the tree 
for this purpose ; but how it is that the oak under these cir- 
cumstances is treated by the insect parent so as to cause this 
outgrowth of its cellular structure [ am unable to explain, 
although it is very evident that the excrescence would not be 
there were it not for the presence of the parasitic ege. 
So it is with the freshwater sponge (Spongilla): there 
are specimens of the same species, as will be seen hereatter, 
in which there is no Spongiophaga Pottsi present, just as there 
are specimens of the sea-water sponge Hircinia in which there 
is no Spongiophaga communis, which Lieberktihn believed to 
be so much a part of the sponge itself that he established his 
genus “ Hilifera” upon this supposed character. I have 
already gone into the history of the subject when treating of 
Spongiophaga communis in the paper entitled “‘ Parasites of 
the Spongida” (‘ Annals,’ 1878, vol. 11. p. 165, with wood- 
cut, p. 168), so need not repeat any more of it here. 
The metamorphoses of parasites are often veiled in almost 
impenetrable mystery until some happy observation renders 
them intelligible. Who, for instance, would have thought 
that the tapeworm came from a Canurus—discharged as an 
egg from one, fostered as Ceenurus in another, and finally de- 
