22 



NA8SA. 



state of the case is exceedingly improbable if not absolutely 

 impossible." 



Mr. Marrat's dilemma is that, whilst disbelieving in species, 

 he cannot pursue his work without naming and describing specie*. 

 It would be impossible to give a full descriptive portraiture of 

 an object every time it is referred to, in order that the writer's 

 conception of it and that of the reader shall agree ; therefore we 

 adopt a conventional system the binomial nomenclature to recall 

 certain characters by the use of two names. I think, however, 

 that it is a logical deduction from the views expressed by Mr. 

 Marrat that his species should not possess such salient characters 

 as those proposed by authors who believe more or less in the 

 doctrine of the persistence of form: if the latter species do not 

 present very strong claims for recognition, the former may be 

 supposed to present no claims whatever, unless we agree that 

 each individual specimen in the genus shall receive a distinct 

 specific name. If there be only one species in the genus Naxxa, 

 as opined by Mr. Marrat, science still requires names for those 

 groups which normally present recognizable distinctive Huir- 

 arcters; without a nomenclature and a system, however arbitrary 

 and unnatural, the publication of the results of scientific research 

 would be impossible. The doctrine of unalterable uniformity in 

 specific characters is overthrown, but a wise conservatism will, 

 let us hope, cause conchologists to refrain from naming and 

 describing every individual specimen: at least, gentlemen, do 

 not overwhelm our ancient and tottering barriers with your 

 logical deluge, until we, who have so carefully erected and 

 guarded them, shall have retired from conchological pursuits. 

 Aprex nous le deluge, if you please ! 



Typical Species. 

 X. MUTABILIS, Linn. PI. 7, figs. 1-3. 



Light brown, with somewhat undulated longitudinal darker 

 markings, generally confluent into a darker interrupted band nl 

 the sutures. Length, 1-1-25 inches. 



Mediterranean Sea, 4 to 10 fathoms ; W. Const of Africa ; 

 Canary Isles, Fossil in the miocene of 8. Europe. 



Upon the embryology of this species see Bobretsky, in Archiv 

 fiir Mikros. Anat., xiii, 97. 



