Character and Distribution of the genus Perigonimus. 487 



Illustrated Catalogne of North American Acalephae. It woiild seem 

 to be limited therefore to what liave been designated as the Littoral, 

 Laminarian, and Coralline rcgions. In only one case has this limit 

 been probablj exceeded, namely in that of P. abijssi, frora a depth 

 otf the west coast of Norway, of 400 fathoms. Again, in only one 

 case has it been reported from other than the coasts of Europe. The 

 description of P. Jonesii from the American coast is the only occur- 

 rence, so far as I am aware, of any member of the genus in these 

 waters. 



Concerning the causes of distributiou relative to Perigonimus 

 little can be said. Propagated by free-swimraing medusae, it is 

 probable that this fact has contributed to its more locai distribution. 

 Its commensal habit may also have similarly aided in extending its 

 ränge, though this has more probably operated against any general 

 extension of ränge, since the host is generally of a somewhat seden- 

 tary habit. So far as the facts at band are of significance, they would 

 seem to point to the origin of the genus in the region of the British 

 Isles, and its very slow transplanting to adjacent and remoter regions. 

 Its occurrence in such remote points as Naples Bay and Long Island 

 Sound must probably be accounted for by causes of a somewhat ex- 

 traordinary character, such as conveyance by ships. 



Such in brief is a sjnioptic glimpse of the more striking character- 

 istics of the genus. That it is tentativo and incomplete in some of 

 its aspects will be recognized in the nature ofthe case. It is hoped, 

 however, that enough has been gathered into the review to aflford a 

 fair introduction to the extremely interesting character of the genus, 

 and to indicate some of the more important morphological problems 

 in its structure and ontogeny. To the latter points I hope to contri- 

 bute further as soon as suitable material cau be secured for in- 

 vestigation. 



Zoological Station, Naples, July 25 th, 1894. 



