CHONDRACANTHCTS DEPEESSUS. 173 



the genital segment. This segment fully one and a 

 half times as wide as the cephalon and its length only 

 about a fourth greater than the width, a distinct 

 transverse constriction dividing the segment into two 

 nearly equal parts which are considerably flattened ; 

 the postero-lateral prolongations moderately short and 

 stout, and blunt at the apex, also distinctly con- 

 vergent so that the apices are usually contiguous, and 

 sometimes overlap each other. Abdomen very short. 



Antennules short and tolerably robust; simple in 

 structure ; the distal extremity, which appears to be 

 obscurely jointed, bearing scattered apical spinules. 

 Antennge somewhat similar to those of Ohondr acanthus 

 cornutus ; the mandibles and maxillipeds also re- 

 sembling those of the same species. Thoracic legs 

 short, stout, biramose, both rami rudimentary, their 

 surface covered with numerous very minute prickles. 

 Length about 5 mm. 



Egg-strings short and stout and containing numerous 

 ova. 



This species has a general resemblance to Chandra- 

 canthus flurae from the long rough dab, but is rather 

 more flattened. 



No males have been observed. 



Habitat. Parasitic on the gills of the flounder 

 (Pleuronectes flesns). Firth of Forth and St. 

 Andrews Bay \T. Scott). Irish Sea (A. Scott). 



This Chondracanthus differs from the other described 

 species by the very short thoracic segment, hy the genital 

 segment being considerably flattened and of a broadly 

 quadriform outline,, and by the structure of the thoracic 

 legs. 



An apparent variety of the species here described, which 

 has been observed parasitic on the same kind of fish, differs 

 in being more elongated and rather less flattened; the 

 thoracic legs are larger and more rudimentary, and the 

 postero-lateral prolongations of the genital segment are 

 scarcely convergent. This form, which has been recorded 

 as variety oblomjiis, appears to he rare (see PI. XLI, fig. 4 ; 

 and PI. LVI, figs. 5-7). 



