THE MOUNT DESERT REGION 215 



There is no 'royal road' to a knowledge of the Crustacea. 

 They yield their secrets only to those who are willing to 

 make the necessary dissections and to attend carefully to the 

 minutiae of structure. Similarly, it is not possible to refer 

 at once to a comprehensive work covering our species and 

 giving complete descriptions and illustrations. For the 

 groups which it covers, G. 0. Sars' ''Account of the Crustacea 

 of Norway" is indispensable. For other works useful in the 

 determination of species the reader is referred to the dis- 

 cussion of the various orders. 



In so large and diversified a group as the Crustacea it is 

 almost unavoidable that the treatment should be somewhat 

 uneven and not equally detailed in all orders. In the present 

 case this is especially true of the benthonic Copepoda. 



Subclass ENTOMOSTRACA 

 Order CLADOCERA 



The two works by Birge and Lilljeborg referred to in the 

 list of literature are in general satisfactory for the discrimi- 

 nation of the American species of this group. The coordinate 

 method of form analysis as exemplified in Rammner's recent 

 papers on Scapholeheris Txingi yields information on variation 

 which was unobtainable by the older methods of description 

 and cannot be overlooked by the serious student. 



Suborder CALYPTOMERA 

 Tribe CTENOPODA 



Sididae 

 Latona Straus 

 L. SETiFERA (0. F. Miiller). (Birge, 1918, p. 690, fig. 1052.) 

 A common fresh-water species. Station : S 23. 



