"(^ tHE CANADIAN ENTOMOLOGIST. 



bb. Head unspotted; punctures of elytral striae finer towards apex. 

 Thorax with black spot anteriorly (. 13-. 14 in.) . . triopsis, Say. 



Thorax immaculate (.16 in.) fasciatus, Aube. 



AA. Thorax with an impressed plica on each side near the base ; smaller 

 species. 

 Pale ochreous yellow; punctuation stronger, thoracic plica 



shorter (.11-. 12 in.) .riificollis, DeG. 



Fulvous ; punctuation less strong, thoracic plica 



longer (.12 in.) lotigulus, Lee. 



Cnemidotus, Er. 

 Our two species are easily distinguished from those of 

 Halipliis by the thorax being ornamented with two black 

 basal spots Mr. Crotch unites under the mxwQ 12-punctatus 

 (fig. 5) the two forms which have been separated on these 

 characters : 

 Hind coxae with a prominent angle on the hind margin 



(• 1 5 in-) i2-punctatus, Say. 



f"'f'- 5- Hind coxaj without this angle (.16 in.) muticus, Lee. 



The next family, the Dytiscid^, is separated with ease from the 

 Haliplidce by the following characters : the body is usually much less 

 stout and convex and more obtuse at the ends ; the antenna^ are eleven- 

 jointed, usually filiform, though occasionally somewhat clavate or thick- 

 ened at middle, inserted under the front behind the base of the man- 

 dibles. The posterior coxae are large, reaching the sides of the body, but 

 not covering the ventral segments. Legs natatorial, ciliate with long 

 hairs. From the Carabidce they may be known by the structure of the 

 hind coxse mentioned above. 



All the species are more or less strictly aquatic in habit, and 9,re as 

 a rule strong swimmers. They may be found in numbers in ponds and 

 water courses, sometimes being seen under the ice after the approach of 

 winter. At night they fly around and are often attracted by lights. Some 

 of the more northern forms, especially of Agabus and Hydroportis, may 

 be taken under wet moss, or beneath stones or boards which have been 

 lying on the grass in marshy places. The sexual modifications in the 

 family are very interesting, the males often possessing a peculiar modi- 

 fication of the anterior (and less frequently the middle) tarsi, whereby 

 the basal joints are dilated into a more or less cup-shaped surface, which is 

 studded beneath with little stalked disks. The number of these disks in 



