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 Scutibranchia. 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 

 being a pulmonated mollusc. The more recent observations of the Rev. G. M. 

 Berkeley! 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 dextral species have been withdrawn by Mr.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 Vettetia, 

 (Acroloxus, Beck;) a division the necessity for which has been questioned, but which, 

 for the reasons stated under the genus Vettetia, I 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, A. 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. A. elcgans (Sow.), from Hordwell; A. depresses (Desh.), from 

 the neighbourhood of Versailles ; A. deperditus (Desmar.), from the fresh-water lime- 

 stone of Ulm; and A. compressus (Nyst), from the neighbourhood of Antwerp. The 

 first two are Vettetia; the descriptions and figures of the last two are insufficient for 

 determining to which genus they belong. 



No. 63. Ancylus r latus. F. E. Edwards. Tab. XIV, fig. 15 a-b. 



A. testa conoided, depressd, lata; vertice submediano : aperturd oblongd, obovatd. 



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. 

 f Ibid., vol. v. 



