APPENDAGES OF THE PEX^EIDEA 



215 



two- or three-jointed eye-stalks, flagella of the first 

 antennae not longer than the carapace, a two-jointed rnan- 

 dibular 'palp,' the third maxillipeds long and pediform, 

 the first three pairs of trunk-legs carrying exopods, the 

 fourth and fifth pairs 

 not longer than the 

 preceding, the pleo- 

 pods with two foliace- 

 ous branches in every 

 pair except the first, 

 which in the male has 

 a large membranous 

 appendage attached to 

 the base. This ap- 

 pendage, called by 

 Spence Bate the pe- 

 tasma or curtain, is 

 rudimentary in the 

 female. In this genus 

 there are no podo- 

 braiichiae. The first 

 species assigned to it 

 by Fabricius was the 

 large Penceus monodon, 

 which occurs in the 

 neighbourhood of Cey- 

 lon, Western Australia, 

 and the Philippines, and is perhaps identical with the 

 Japanese Penceus semisulcatus of de Haan. Penceus cara- 

 inote (Risso) is found in the Mediterranean and Atlantic, 

 and is sometimes taken in English waters. 



Penceus canaliculatus, Olivier, appears to extend with 

 little variation from Japan to Australia, and to differ only 

 in small particulars from Penceus caramote. Thus, it has 

 nine teeth instead of twelve on the dorsal crest, straight 

 instead of wavy ridges on either side of the carina of the 

 carapace, the spine on the outer margin of the first joint 

 of the first antennae not nearly instead of quite reaching 

 the extremity of the eye, no tooth on the second joint of 



FIG. 20. Sergestes Atlanticus (Milne-Edwards), first 

 pleopods of the male, with petasmata united in 

 the median line [Sp. Bate.]. 



