110 EOCENE MOLLUSCA. 
water, and assumed that this was for respiration, also placed the genus among the 
aquatic Pulmonata. On the other hand, Lamarck and Blainville, although they adopted 
the genus, retained it, provisionally, the former, among the Calyptracea, the latter 
among the Seutibranchia. Subsequently, the Rev. Mr. Guilding, in his ‘ Zoology of the 
Caribean Islands,* gave the generic characters of the animal, and described the 
respiratory apparatus as consisting of a small branchial plume placed on the left side, 
near the excretory orifice; and M. Deshayes, misled by this description, has, in the 
2d edition of Lamarck’s ‘ Histoire Naturelle,’ rejected the supposition of the animal 
bemg a pulmonated mollusc. The more recent observations of the Rev. G. M. 
Berkeleyt have shown, however, that the animal, in its organs of respiration, resembles 
those forming the present order, and that it is, in fact, a true pulmonated mollusc. 
The respiratory orifice is protected by a valvular enlargement of the margin of the 
mantle, which, it is conjectured, was mistaken by Mr. Guilding for a branchial plume. 
The genus, as originally proposed, embraced as well dextral as sinistral species. The 
dextral species have been withdrawn by Mr. Gray, under the generic name /e/letia, 
(Acroloxus, Beck;) a division the necessity for which has been questioned, but which, 
for the reasons stated under the genus Vell/etia, 1 have adopted, and the present genus 
is therefore confined to the sinistral species. 
The animal is hermaphrodite, but the union of two individuals is necessary for 
fecundation: the head is furnished with two cylindrical or triangular retractile ten- 
tacles, oculated at their bases; the foot is short, and attached to the abdominal mass, 
and the mantle is large and free, with a simple continuous margin. The living species 
are not numerous; one only, 4. fluviatilis, is found in this country and in central and 
southern Europe; the rest occur principally in central America. They live in fresh- 
water, preferring gentle streams. 
Four fossil species have been described and referred to this genus, all from the 
Eocene formations, viz. 4. elegans (Sow.), from Hordwell; 4. depressus (Desh.), from 
the neighbourhood of Versailles; 4. deperditus (Desmar.), from the fresh-water lime- 
stone of Ulm; and 4. compressus (Nyst.), from the neighbourhood of Antwerp. The 
first two are Ve//etig; the descriptions and figures of the last two are insufficient for 
determining to which genus they belong. 
No. 63. ANcyLtus? tatus. /. #. Edwards. Tab. XIV, fig. 15 a-d. 
A. testa conoided, depressa, lata; vertice submediano : apertura oblonga, obovata. 
The imperfect state of the only specimen I possess, prevents my doing much more 
than to record the occurrence of this shell, which I refer to the present genus with 
hesitation. It is distorted at the posterior extremity, and presents the appearance of 
* © Zoological Journal,’ vol. iii, p. 535. 
+ Ibid., vol. v. 
