Archer — On Freshicater Rhizopoda. 
87 
and even essential, that this problematic ' skin ' mnst, in fact, 
possess such an extensibility and elasticity, that it becomes ultimately 
broken through by bodies pressing against it, be it from without 
inwards by inception of food, or be it by projected pseudopodia. Eut 
just as undoubted and essential is it also, that subsequently, as well 
following the incepted food-particles, as after the pseudopodia are again 
retracted, the breaches which had taken place should become at once 
again restored, through the elasticity and easy fusibility of the skin. 
I was not able to find a nucleus in the interior of the granular 
parenchyme, but, however, some minute contractile vesicles ; its 
dimensions reach a diameter of 0-04™." 
This, then, is all Greeff gives us in connexion with these interesting 
forms. It is a pity his account of the two latter forms is so short, 
but should they turn up in other quarters, his figures would most 
likely render the identification not difiicult. It is perhaps also, to a 
certain extent, a pity that he calls the outer coat by such varied names 
as Hiille — Schale — Haut — Kapsel — Saum," &c., when, perhaps, the 
more general term ''Hiille," might at least be preferable, that part 
of the structure being at all events one and the same thing throughout. 
Combining, however, what we have learned respecting my own new 
form, brought forward on the present occasion, with what Greeff has 
communicated of the three he has named, we gain a conception of a 
seemingly distinct generic type of rhizopod, previously to his memoir, 
not recorded, at least not defined, and one of considerable interest. 
It may look somewhat like temerity, on my part, to essay to do 
what Greeff has unfortunately left in abeyance ; that is to try to 
comprehend in a diagnostic form what appear to be the characteristic 
or essentials of this genus, so far as observation reaches. 
Genus, Amp'hi%onella (Greeff). - 
Generic Characters. — Rhi%opod, with a nucleated'''' hody-mass, en- 
closed in a distinct {and separalle), more or less pellucid, elastic and y ield- 
ing investment, through ivhich it temporarily protrudes a greater or less 
number of digitate or tapering, short, hyaline pseudopodia, upon the re- 
traction of which the extemporized openings in the investment lecome effaced 
hy virtue of its inherent fusihility. 
Affinities and Differences. — The nucleus" and the digitate, or 
short tapering pseudopodia presented by the forms appertaining to such 
a genus as the foregoing diagnosis may, perhaps (so far as present in- 
formation goes), successfully define, seem at once to stamp its '' Amoe- 
ban" afiinity. There might be thought to be some resemblance — nay, 
close afiinity, to Greeff' s Astrodisculus,^* but the want of the so-called 
* Greeff, " Ueber Eadiolarien und Badiolarien-artige Rhizopoden des siisseu 
"Wassers," in Schultze's " Archiv fiir mikrosk. Anatomie." — Bd. iv. p. 496. 
t. xxvii. 
