CALIGOIDEA. 1353 



3. In the shape of the abdomen, the female often having the broad- 

 est or the longest abdomen. 



The sexes are similar in the other organs, and very nearly so in 

 the position and size of the stylets of the abdomen. 



In Milne Edwards's Histoire Naturelle des Crustaces, the anterior 

 abdominal segment is considered a part of the thorax ; and in com- 

 paring our descriptions, it should be noted that we consider it as pro- 

 perly corresponding to the second (or first and second) segments of the 

 abdomen, the second being the one in the Cyclopoidea and this group 

 of Entomostraca from which the external ovaries proceed. 



Caligus Thtkni. 



Carapax oblongus. Abdomen 2>-articulatum, segmento primo lato, 

 sequentibus duplo latiore, ano valde prominente. Styli caudales par- 

 vidi, ad angulos abdominis posticos insiti, anum vix superantes. An- 

 tenna? posticw spind extus basin non munitce. Furcula simplex, 

 brachiis divergentibus, subacutis. Feminae -.^—Abdominis segmentum 

 primum oblongum, lateribus rectis et postice parce divergentibus, 

 angidis posticis prominentibus ; segmentis duobus sequentibus simul 

 sumtis elongatis, et fere longioribus. Maris : — Abdominis segmentum 

 primum subquadratum, angulis posticis vix prominentibus, segmentis 

 sequentibus sim,ul sumtis brevioribus. 



Carapax oblong. Abdomen three-jointed, first segment broad, twice 

 broader than the following, the anus quite prominent. Caudal 

 stylets small, filling out the posterior angles and hardly projecting 

 beyond the anus. Posterior antennae without a spine exterior to 

 base. Furcula simple, prongs divergent, pointed. Female: — Ante- 

 rior abdominal segment oblong, sides divergent, posterior angles 

 prominent, following part longest. Male: — Anterior abdominal 

 segment nearly quadrate, posterior angles scarcely prominent, the 

 following part shortest. 



Plate 94, fig. 3 a, ventral view of male, enlarged ; b, posterior an- 

 tennae of female ; c, abdomen of female. 



839 



