BY H. LEIGHTON KESTEVEX. 451 



related " in this discussion; but it is not argued that any one 

 species is more nearly related to any one other than to the rest. 

 Such a line of argument, were it substantiated, would prove 

 disastrous to my contention, for community of relationship pre- 

 supposes community of descent. Were it possible to prove a 

 common progenitor for any group, distinct from that of another, 

 it would certainly be advisable to separate such, at least sub- 

 generically. I would suggest that the groups are to be accounted 

 for by variation along similar lines from the original parent. 



The four genera of Dall and Simpson are Sejyta^ Ranularia, 

 Lampusia and Lotorium. Being full genera it is important that 

 they should be discussed. The descriptions given with the 

 rehabilitation of each of these are not sufficient to define them; 

 there is, however, another way of determining their value. On 

 comparison with sections previously proposed they appear to equal 

 those of Try on. 



Septa can be no other than Triton (sens. sir.). Two out of the 

 three species enumerated under Lampusia occur in Simpulum. 

 Lotorium evidently equals Cymatium. The species named under 

 Ranularia is placed by Tryon in his subgenus Gutturnium. That 

 this is an unsatisfactory way of deciding the matter must be 

 admitted, but it receives support from the fact that there are 

 only four divisions in each work (though Tryon divides his sub- 

 genera into groups), and that Septa could not have been applied 

 to the tritonis-gvoM'^ had not these authors accepted Tryon's 

 classification of L. parkinsoniamcm, Perry ( = X. fusiforme, 

 Kiener). If, however, this deduction is incorrect, and Dall and 

 Simpson's genera do not equal Tryon's subgenera, the following- 

 statements will not be invalidated. It is submitted that they 

 serve to prove that the group known of old as Triton is a natural 

 genus and cannot be divided. The specific nomenclature here 

 employed is that of Tryon's " explanation of plates " as a read}'- 

 means of intimating to my readers the particular forms referred 

 to; not that I entirely disagree with his synonymy. The values 

 of a few specific names are dealt with in the concluding i^art of 

 the paper. 



