F. Dixon — Mesenteries of the Genus Sagartia. 141 



to species too widely differing to be grouped together, and proposed 

 that S. venusta should be made the type of a genus which should 

 retain the name Sagartia. The close affinities existing between 

 S. miniata, S. nivea, S. rosea, and S. venusta, show that these forms, 

 at least, must be referred to a single genus, and the laws of pri- 

 ority in nomenclature compel us to keep for this genus the name 

 Sagartia. But these four species have been shown to have an 

 irregular number of numerous perfect mesenteries, and therefore 

 cannot be included in the family Sagartidce, as re-defined by Pro- 

 fessor Hertwig ; so that if we give the name Sagartidce to Professor 

 Hertwig's family, we shall have to exclude from it the genus from 

 which it gets its name. 



As this step is inadmissible, it is clearly necessary either to 

 extend Professor Hertwig's definition so as to include the genus 

 Sagartia as above limited, as well as the genera with the arrange- 

 ment of mesenteries discovered by Professor Hertwig, or else 

 accepting his definition to change the name, leaving the term 

 Sagartidce for that family which will include the genus Sagartia. 



[Explanation of Plates. 



