OF NEW SOUTH WALES. 63 



there are generally a few diagonal yellow lines which make the 

 spot still more conspicuous, especially as the enamel of the rest 

 of the shell is such a thick glossy lining of intense brown, almost 

 like the varnish known as Brunswick black. 



The shape of the species and varieties is very uncertain. 

 Sometimes the shell is almost turbinate, and the whorls rounded ; 

 in others it is depressed, the whorls ovately angular, smooth, and 

 flat ; others again are more depressed, and the whorls almost 

 keeled with tubercular undulations on the edge, which become 

 almost spinous. At times also the spire is ornamented with 

 coarse nodular protruberances. Now, seeing all these variations 

 we are bound to enquire on what is the generic distinction to 

 rest. Not on the shape or ornamentation of the spire, nor on 

 the depressed or angular sharpness of the whorls. Not on the 

 funicular basal thickening, for that is uncertain too. In any case 

 it would be a genus with one species, but a species which in no 

 respect can be divided generically, from typical Littorince. The 

 animal is the same ; the operculum is horny, pauci-spiral, with a 

 marginal nucleus. The odontophore is the same, and curled in 

 a coil at the back of the head ; there are no tentacular 

 appendages. The shell is not nacreous, and the habits of the 

 animal are in all respects those of Littorma. It lives almost 

 always out of the water, on rocks exposed to the spray. It is 

 found in brackish water, and can bear the extremes of heat and 

 cold. 



Messrs. Adams reminds us in the Annals of Nat. Sist. that no 

 harm is done to science by the addition of a new genus, and this 

 is quite true as long as it is founded on well defined and 

 permanent features. But if a genus is erected on characters 

 that are slight and uncertain, and if, moreover, they vary and 

 pass insensibly into others, then it is an injury to science and to 

 the student, who will be bewildered in trying to recognise them ; 

 an injury also to any sound system of classification. For these 

 reasons, therefore, I think most scientific men will agree with 

 me that the genus Risella ought to be suppressed. It has no 

 permanent characters which can be relied upon to separate it 



