338 SPECIES OF THE SYSTEMA. 
this little species. Chemnitz has omitted it; Gmelin has merely 
transcribed its diagnosis; Schréter has rested content with 
noting the incongruity of locating a smooth shell in a cancel- 
lated section. Dillwyn, with some reason, suspected that it was 
identical with the Valvata piscinalis, but the contour of that 
shell is orbicular-conic, this is said to be ‘ oblongiuscula.” 
Philippi, on the contrary, believes it (Moll. Sicil.) to be the 
same with his Paludina muriatica,—of which he regards the 
P. (Cyclostoma) acuta of Draparnaud to be a synonym,—princi- 
pally because of its having been found in warm baths; the 
expression of our author, however, was not “In thermis,” but 
“prope Thermas Pisanas,” and the “apertura orbicularis” of 
the ‘Systema’ is too much at variance with the “apertura 
ovata, superne distincte angulata”’ of the German naturalist to 
be passed over. For a like reason the identification of the shell 
by Potiez and Michaud (Palud. thermalis, Gal. Douai, Mol. 1. 
pl. 26, f. 29) cannot be assented to. 
A rather important aid seemed promised us by a manuscript 
reference of our author to “ Vandel. Patay. p. 115, pl. 3, f. 1;” 
the engraving, however, is far from good, yet reminds us of 
Bithinia ventricosa and of Draparnaud’s drawing of Paludina 
similis (consideredby many as the same species). Our native 
Bithinia, indeed, approaches the description very closely, but 
no sound identification (so far, at least, as to affect the name) 
can ever be based upon the mere accordance of a shell with 
a brief diagnosis and an unpublished reference to a rude 
engraving. We learn from the text which accompanies the 
above-mentioned figure, that the shell delineated was only as 
large as a grain of millet, twice as long as broad, bluish white, 
composed of four volutions, the last-formed of which was 
decidedly big, the two preceding nearly equal in size to each 
other, and the apical turn abruptly diminished to an acute 
point: the aperture (represented in the engraving as occupying 
two-fifths of the total length) is stated to be a segment of more 
than half a circle. No shell which answers to this description 
can be found in the Linnean cabinet, and in truth the account 
of the aperture scarcely allows us to imagine that the object 
thus described, although in general look and local peculiarity 
it resembled thermalis, was really the shell intended by Linneus. 
The reference, however, to Vandel, so far defines the species, 
