1S75.] molluscan Genera Coelostele and Francesia, Sfe. 43 



hitherto been found), have their surface more or less dirty and their orifice 

 filled with detritus, the reverse being the case with fluviatile species. 



Issel, who collected the Aden specimens, in a paper published* soon 

 after that by Paladilhe, gives his reasons for disputing the systematic posi- 

 tion assigned to Francesia by its author, and for considering it a terrestrial 

 and not a fluviatile mollusk. In his opinion it belongs to the Helicidce, 

 and is allied to Bulimus. He points out certain characters which it has 

 in common with Stenogyra, Ccecilianella and Fnnea.f I think that there 

 can be very little doubt as to the correctness of Issel' s view so far as the 

 terrestrial nature of the mollusk is concerned, and that his opinion of its 

 affinities to the Helicidce are more probable than Benson's supposition that 

 the genus belongs to the Auriculidce, or Paladilhe's that it should be as- 

 signed to the neighbourhood of the Lymnceidcs. I cannot see that the 

 absorption of the spiral axis, the character upon which alone Benson appears 

 to have relied, is sufficient evidence of affinity, because it is found in gaste- 

 ropodous genera belonging to widely different families, e. g., in JVerita, 

 and there is no other character in which the shell of Ccelostele scalaris 

 is shewn to have any close resemblance to Auricula ; whilst the reason 

 assigned by Paladilhe for supposing his genus Francesia fluviatile, the com- 

 plete freedom of the shell, and especially of the orifice, from clay or sand 

 is certainly an insufficient argument, at all events in those countries in 

 which Ccelostele has hitherto been found. I have just examined a small 

 collection of minute shells, picked out from flood deposits in Sind, and 

 amongst them I have found several specimens of Blanorbis and Bythinia 

 with their aperture filled with sand, whilst this appears to be very rarely 

 indeed the case with the minute Achatina balanus of Benson, a species 

 which Paladilhe assigns to Francesia, but evidently without having a clear 

 idea of the species, for he, immediately afterwards, unless I am greatly 

 mistaken, redescribes it as a new species under the name of Ccecilianella 

 Isseli. 



It is very singular that the animal of A. balan us should never have 

 been observed and that we should be as much in doubt about its real 

 affinities as we are about those of Ccelostele. I am strongly disposed to believe 

 that it is very closely allied to a shell described by Crosse from New Cale- 

 donia under the name of Geostilbia Caledonica.% The figure representing this 

 form might almost be mistaken for that of Achatina balanus, but the geogra- 

 phical position of Geostilbia Caledonica is unfavorable to its identification with 



* Ami. Mus. Civ. Gen. IV, p. 521. 



f This genus does not belong to the Helicidce but to a distinct family. Conf. Dohrn, 

 Malakoz. Blatt. XIII, p. 129 ; and Stoliczka J. A. S. B., 1871, XL, pt. 2, p. 159. 



% M. Crosse very kindly gave me a specimen of this shell, but I have unfortunate- 

 ly left it in England and am unable to compare it with Achatina balanus, 



