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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVIII. 



But the regions of the cephalo-thorax are practically the same and 

 are very similarly arranged in the two. 



As boundaries of these regions we find grooves similar to those in 



the Argulidee but differently arranged, not 

 merely in the different genera, but in dif- 

 ferent species as well. 



In general they ma} 7 be described as fol- 

 lows: A pair of longitudinal grooves, one 

 on either side of the mid-line, more or less 

 parallel with it and removed some distance 

 from it, correspond with the sides of the 

 horseshoe suture in the Argulidse. 



But they extend backward farther, 

 reaching the posterior margin of the lateral 

 lobes, while they do not reach forward to 

 the frontal margin. The} 7 form the sides 

 of a large letter H and are connected by 

 the third groove transversely at or just 

 posterior to the center of the carapace 

 (fig. 2). The carapace is hinged along 

 these sutures and capable of some motion 

 upon them, as in the Argulida?. On the 

 outside of the lateral grooves are the lateral 

 areas, extending back in a lobe on either 

 side of the carapace much narrower than in 

 Argulus (L. A.). 



The transverse suture marks the junc- 

 ture of the head and thorax so that the 

 central region in front of it is the cephalic 

 area(C. A.), while behind it is the thoracic 

 area (T. A.), the former being usualby the 

 larger. These three grooves are present in 

 practically all the genera and species. In 

 addition there are others which occur with 

 more or less frequency. One of these is a 

 horseshoe-shaped groove extending from 

 the suture between the carapace and the 

 frontal plates backward around the eyes. 



It is similar in shape to that in the Argu- 

 lida?, but as the eyes in the two families 

 are entirely different it does not corre- 

 spond in morphological significance. 

 There are also grooves at the bases of the free portions of the first 

 antennae which extend inward on the carapace for a short distance, 

 while others appear often in the anterior portion of the lateral areas. 



Fig. 2. — Adult female of Caligus 

 mutabilis, showing the body 

 regions and the areas of the 

 carapace, a., abdomen; c a., 

 CEPHALIC AREA; E. S., egg-strings; 

 F. P., FRONTAL PLATES; F. S., FREE 

 THORACIC SEGMENT; G. S., GENITAL 



segment; L. A., lateral areas; 



T. A., THORACIC AREA. 



