NORTH AMERICAN PARASITIC COPEPODS BELONGING 

 TO THE FAMILY CALIGID.E. 



PART 2.— THE TREBIN/E AND EURYPHORIN/E. 



By Charles Branch Wilson, 



Department of Biology, State Normal School, Westjield, Massachusetts. 



INTRODUCTION. 



This fourth paper in the series based upon the collection belonging' 

 to the United States National Museum is reall}' a continuation of the 

 third, which was published in Vol. XXVIII of these Proceedings. 



It takes up the second and third subfaujilies of the Caligid^ and 

 includes the five species belonging to these subfamilies which have thus 

 far been found in North American waters and three which are foreign, 

 but at the same time are represented in the Museum collection. 



Of the five native species one, Dysgamus arlommus, is new to sci- 

 ence; the others have, been described elsewhere, but three of them, 

 Gloiopotes ortiatus^ Aleblon gracilis, and Alehion glaber, have never 

 before been figured. 



In conformity with the policy adopted for this series of papers, the 

 artificial keys under the subfamilies and genera, which are here for 

 the first time presented, are made to include all the known genera and 

 species, respectively. 



Since both the subfamilies here treated are new to science, their 

 ontogeny is also new. This is especially true of the continuous life- 

 history of the genus Alehion, with the figures of its metanauplius and 

 the anotomical details of the latter, upon which is based the raimn 

 d'etre of the subfamily Euryphorinje. 



Svibfamily TRE;BI]Sr.^EC. 



Sexes similar as in the Caligin;^. First and second thorax segments 

 united with the head to form a broad and flattened carapace. The 

 various regions on the dorsal surface separated by distinct grooves 

 arranged difi'erently from those in the other subfamilies. Third and 

 fourth segments free and without dorsal plates or any appendages 



Proceedings U. S. National Museum, Vol. XXXI— No. 1504. 



669 



