Operculum o/'Georissa. 175 



tlie numerous species classed with it by PfeifFer, II. and A. 

 Adams, and Gray. The latter, in the British-Museum Cata- 

 logue, places it in Realia ; Pfeiffer, who is followed by H. & 

 A. Adams, retains it as the type of a genus which he places 

 next to Realia^ but associates with it a number of species be- 

 longing, some of them, as Von Martens shows, to Assiminea, 

 others to O)nj)halotropis* or an allied genus. It is curious 

 that Pfeiffer, who usually attaches rather too much importance 

 to the characters of the operculum, should have overlooked 

 the peculiarities of that of Hydrocena cattaroensis^ which he 

 simply describes as " Operc. paucispirum, rubellum " (Mon. 

 Pneum. Viv. Supp. i. j). 160), although it is figured by Klister 

 in the second edition of 3Iartini and Chemnitz, ani the de- 

 scription and figure are quoted by Pfeiffer f with his usual 

 accuracy. The operculum is in almost every respect similar 

 to that of Oeorissa ; and as Kiister's description of the genus 

 appears to have been generally overlooked, it may be as well 

 to append a translation of it, in order to show the connexion of 

 the two genera. The description, in German, occurs at p. 80 

 of part I. 21, of Martini and Chemnitz: — 



" Shell small, imperforate, conical, thin, with a broad conical 

 spire, scarcely exceeding the apertui'e in height ] the whorls 

 few in number, slowly increasing, convex. Aperture ovate, 

 angulate above as in Paludina^ edges united by a thin callus 

 resting on the penultimate whorl ; peristome straight, not ex- 

 panded or thickened ; columella somewhat concave, with a 

 free reflected edge below ; umbilicus filled by a callus, which, 

 when highly magnified, exhibits a very fine granular wrinkled 

 sculpture (as mXeritina). 



" The operculum is of peculiar construction, widely different 

 from that of Paludina %. It is calcareous, and has a nucleus, 



* In the orioinal publication of his ' Monographia Pneumonopomorum 

 Viventium,' Pl'eifFer quite correctly excluded Hydrocena cattaroensis flora. 

 the Cyclostomacea, retaining Omphalotropis nihens, Quoy & Gaimard, and 

 its allies, which belong to the order, unless, as is possible, they are teiTes- 

 tiial Rissoidse. It is sti-auge that in the first supplement to the mono- 

 gi-aph, after Kiister and Troschel had described and figured the animal 

 and tongue of Hydrocena, Pfeiffer should have reintroduced it amongst his 

 Cyclostomacea, and have retained it in the same position in the second 

 Supplement. 



t Pfeiffer, in his second Supplement, refers to a description of the ani- 

 mal of Hydrocena by A. Adams, in the Ann. & Mag. Xat. Hist, for 18G1, 

 vol. vii. p. 19(5. The aniniiil there described, however, is that of one of 

 the land-shells allied to Omphalotropix which have been incorrectly 

 referred to Hydrocetui. 



X Hydrocena is classed with Paludina and Valrata in Kiister's Mono" 

 srranh. Hence the allusion:'. 



^^ 13* 



