1324 



CRUSTACEA. 



times also they are placed one alongside of the other. In the genus 

 Lepidopus, the finger is wanting, and the preceding joint has a large 

 flat surface below, which is set with scales, each scale having a minute 

 point at apex (Plate 92, fig. 5/). In Argulus alone, the leg though 

 stout is elongate, and not prehensile, and has a more ordinary pedi- 

 form character, ending in a small claw. 



Preceding the third pair of feet, or first natatory pair, there is often 

 a furcate corneous process on the venter, pointing backward. 



The third pair of feet, or first pair of natatories, is the smallest of the 

 natatory feet in the Caligidae, though hardly less than the following 

 in the Argulidse. It is either simple or two-branched, and is fur- 

 nished with a few setae. In Argulus, the two branches are long and 

 plumose, and there is a third branch which is two-jointed, and lies 

 reflexed alongside of the basal portion of the leg. 



In the Dichelestidse, the eight natatories are nearly similar, having 

 two branches furnished with setae, as in Ergasilus and Corycaeus. 



The second pair of natatories in Argulus is like the first. In Cali- 

 gus it is much larger and stouter, and always two-branched. The 

 branches are two- or three-jointed, and furnished with setae, which are 

 quite long and plumose in some genera, and the setae of the inner 

 branch in such species extend inward over the venter when at rest. 

 The terminal seta of the outer branch, as in the Cyclopoids, is ensi- 

 form, and only ciliated on the lower edge. 



The third pair of natatories in Argulus resembles the second, except 

 that the reflexed branch is wanting. In a few Caligidae, also, it is 

 near the second pair in structure; but in most of them it is expanded 

 into a very broad, lamellar form, having the two branches very short 

 and attached to the margin. The legs of the two sides, when thus 

 modified, are often united together by a free lamellar sternum, so as 

 to form a large apron-like appendage, which unites with the margin 

 of the shell around in giving a close attachment of the body to any 

 supporting surface. The cavity beneath the body is thus completely 

 closed in, and water may be retained within, and thus sustain the 

 animal, although out of water. To give strength to the articulation 

 of this moveable apron, a pair of slender corneous processes extend 

 backward from the sternum of the preceding pair (see fig. 1 q, Plate 

 93) to the sternum of the apron, which has a corneous anterior 

 margin. 



The fourth pair of natatories is more variable. In Argulus and 



