310 APPENDIX. 
This is not very rare at Clacton; at Copford, Mr. Brown tells me, it is so. It closely resembles H. 
rotundata in its large umbilicus and elevated ridges, but is justly separated from that species by well-marked 
characters, having large yolutions, which are fewer in number, and the aperture is consequently more open. 
H. striatella, Anthony, ‘Bost. Journ. Nat. Hist.,’ vol. ili, p. 278, pl. 3, fig. 2, an existing species in the United 
States, is now admitted to be the same as the above; and H. perspectiva is, perhaps, only a variety. A 
species, with a geographical range extending from Russia and Switzerland to Massachusets and Ohio, 
might be expected to possess considerable variation.* In my List of Land and Fresh-water Shells from the 
Older Tertiaries, at Hordwell, published in the ‘Lond. Geol. Journ.,’ vol. i, p. 118, I had considered a species 
found there to have prolonged its existence unchanged to the present time, and that the one above referred 
to (striatella) was its specific descendant. Mr. F. Edwards, in his ‘Monograph of the Eocene Moll. 
Pulmonata,’ p. 66, gives his opinion adverse to that decision ; and I am now inclined to think he is correct. 
H. labyrinthica was given in my list as one of the species existing at the present time, while two others 
were also inserted there, but with a doubt. I was at one time impressed with the idea that an air-breathing 
molluse, being less exposed to a variation of conditions, was enabled to preserve a specific existence longer 
than its marine brethren ; and I fear it gave a slight bias to my determinations. Mr. Edwards has bestowed 
upon the labyrinthica a very critical and a very able examination, and has pointed out some differences 
between the Hordwell fossil and the existing American shell ; but they were not, he considered, sufficient to 
invalidate their identity, more especially as the living shell is itself subject to considerable variation ; 
assuming, also, that if we possessed a large series of fossil specimens, these differences would probably 
disappear: is it really certain that the possession of a larger series must necessarily bring the recent and 
fossil nearer together? This species of mollusc appears to stand almost, if not entirely, by itself, as dating 
its existence from the Older Tertiaries; and, as we are obliged to depend exclusively upon the restricted 
characters of the shell alone, we are compelled to admit its identity, from the impossibility of pointing out a 
dissimilarity such as is generally considered sufficient for specific separation. Might it not be possible 
that the combined characters of the entire animal, could they be possessed, would exhibit a difference so as 
to prevent its coming within the definition of a species in the present acceptation of that term? If this 
Hordwell fossil be really still an existing shell, it militates somewhat against the hypothesis that a species 
with a very prolonged existence in regard to time, would, if still in being, have a more extended geo- 
graphical range, and vice versa ; it does not appear so in regard to Helix, when labyrinthica is compared 
with ruderata. 
SIPHONOSTOMATA. 
Mirra EBENUS, Lamarck. ‘Tab. XXXI, fig. 7. 
Mirra EBENUS. Lam. Ann. du Mus., vol. xvii, p. 216, No. 58, 1822. 
— — Phil. En. Moll. Sic., vol. i, p. 229, t. 12, figs. 8—10. 
— _ Bellardi. Monog. delle Mitre Foss. del Piedmonti, p. 23, t. 11, figs. 
20—23, 1850. 
— PYRAMIDELLA. Bronn. yar. 8. Ind. Paleonth., p. 733, 1848. 
— pLumMBEA. Lamk. Hist. des An. s. Vert., tom. vii, No. 73, 1822. 
* This is the only one of the six extinct species belonging to these Fluviatile deposits that has its range 
to the westward; the others belong to the European Continent, with the exception of Cyrena consobrina, now 
an inhabitant of the Nile. The Mollusca of these beds do not appear to have any connection with the 
peculiar, and probably more recent, Faunas of the Canaries, Madeiras, or the Azores. 
