Occasional Papers of the Museum of Zoology 5 



admissible evidence. It may, therefore, be considered as set- 

 tled beyond dispute that Pleurocera since 1819 has been an 

 adequately described genus, representing a common and well 

 known group of species and as such it has been universally 

 recognized for more than fifty years. 



It is equally clear that Pleurocera verrucosa Raf. does not 

 fall within the original generic diagnosis nor agree with 

 Rafinesque's figure, but, on the contrary, by the unanimous 

 concensus of opinion of all conchologists for over half a cen- 

 tury, belongs to an entirely different genus. 



Pleurocera belongs to category 5 of Opinion 46 of the In- 

 ternational Commission. 



Three rules are laid down in that opinion : 



1st. "In genera published without mention, by name, of 

 any species, no species is available as a genotype unless it can 

 be recognized from the original generic publication." 



That is, no species that does not comply in its characters 

 with the original generic diagnosis, is available as the genotype. 



2nd. "If it is not evident from the original publication 

 of the genus how many or what species are involved, the genus 

 contains all the species in the world, v/hich would come under 

 the generic description as originally published." 



3rd. "The first species published in connection with the 

 genus becomes ipso facto the type." 



My contention is, that these rules of procedure must be 

 construed together and harmoniously. Any construction that 

 v.ould so interpret any one of these rules as to negative either 

 of the others must necessarily be erroneous. In short, if the 

 "first species published in connection with the genus" does not 

 comply with the generic diagnosis and therefore cannot "be 

 recognized from the original generic i:)ublication," it is not 

 available as a genotype. 



