64 THE PEOCEEDINGS OF THE LINNEAN SOCIETY 



from lAttorina. It is simply one of our Australian Littorince, 

 very determinate and characteristic, though within certain limits 

 very variable. It seems that it has a very wide range, and 

 though specimens from extreme portions of the continent would 

 with difficulty be recognized as the same, yet they are all one 

 species flourishing under different conditions. In thus suppress- 

 ing the genus Risella we are really simplifying the science. I am 

 aware that the principle of suppressing genera which graduate 

 insensibly into one another must not be pressed too far. Thus 

 it would be difficult to draw a distinct line between such 

 apparently well established genera as Turbo and Trochus. M. 

 Deshayes acknowledged this when he tried to distinguish them 

 by the calcareous or horny operculum, or by their being nacreous 

 or non-nacreous. But all these features are interchanged. A 

 better distinction might be found to rest upon the odontophore 

 or lingual ribbon, but even this is insufficient. But difficulties 

 like these are not in question in the case of a genus with only 

 one species, where the characters on which it is founded appear 

 and disappear in different individuals. Littorina melanostoma is, 

 however, a very good and interesting species, and may be taken 

 as one of those forms which give a character to the Australian 

 fauna. It is said to extend to New Zealand, at Auckland, though 

 Oapt. Hutton says the locality is doubtful. This species has 

 been re-described in the cruise of the Novara as B. Kielmanseggi. 

 The following will be the synonomy of the species : — Trochus 

 in fauce nigerrimus, Chemnitz, Conch. Cabinet, t. 5, p. 20, pi. 

 161, /. 1,526, a.b. (I cite this and the three following on 

 the authority of Deshayes, in Lam. 2nd edit., though far from 

 sure that they refer to the species, t) Trochus, Schrot, Einl. 

 I. 1, p. 682, n. 12. Trochus melanostomus, Gmelin, p. 8,581, 

 No. 90. Dillwyn Catalogue, b. I. 2, p. 797, No. 89. Deshayes 

 Lamarh, Vol. 9, |:>. 157, No. 78. Trochus nanus, ibid., p. 150, 

 No. 67. Littorina luteola, Quoy., Voy. de V Astro, torn. 2, p. 4i77, 

 •pi. 33, /. 47. Bisella aurata, Quoy. ; Risella nana, Quoy. ; R. 



* i Risella varia, Hutton, is given by him as Adeorbis in Jour, de Conch., 1878, p. 27, 

 Vol. — . Marten considers it a Risella. 



t It may be that the origin of the name is from Reeve, Proc. Zool. Soc., 1842, p. 185, 

 as Trochus. 



