TIRONIDAE 153 



cutting edge, large dentate secondary cutting plate in left only, no spine row or molar, 

 palp 3-jointed, 3rd joint shorter than 2nd. Lower lip without inner lobes, outer lobes 

 acuminate. Maxilla 1, inner lobe horizontally projecting inwards, much smaller than 

 outer lobe, which has 15 spines on inner margin, palp with 2nd joint enormously en- 

 larged to form a curved plate. Maxilla 2, both lobes projecting inwards. Maxilliped, 

 outer plate not greatly exceeding inner plate, and placed laterally to it, not overlapping 

 it, palp well developed, extending beyond apex of outer plate. 



Gnathopods 1 and 2 simple, 5th and 6th joints broad. 



Peraeopods 3-5, 2nd joint not strongly expanded. 



Remarks. This genus seems closely allied to Alexandrella, Chevr., but deserves to be 

 kept separate on account of the presence of eyes, the shape of the maxilliped, and other 

 less important differences. 



The mandibles and enormous maxillary palp are reminiscent of Pardalisca, but no 

 doubt the similarity of these features is due to similar habits of life. 



Alexandrella dentata, Chevr., was found in a sponge in the Antarctic regions, but there 

 are no data with the present specimens as to how they occurred, except that they were 

 caught in the young-fish trawl ; they were, however, accompanied by typical pelagic 

 Hyperiids and other pelagic organisms, and are therefore presumably also pelagic or 

 bathypelagic. 



The very complete protection of the mouth-parts seems to imply some special 

 habitat. The maxillary palps fold over the mandibles, and the 1st side-plates fold over 

 the maxillary palps. Farther back the buccal chamber is closed in by the maxillipeds 

 and especially by the gnathopods; the thick fringes on the margins of these appendages, 

 especially that on the hind margin of the 2nd joint of gnathopod 2, being obviously 

 intended to strain off particles of foreign matter. Finally the 1st and 2nd peraeopods 

 complete the protective arrangement. The nature of the bottom at the neighbouring 

 station 274 is recorded as being muddy. 



The large eyes indicate a mobile mode of life and the oar-like dactyl of peraeopod 5 

 seems to point also to a free-swimming mode of life. 



Whether both Alexandrella and Cacao are rightly placed in the Tironidae may be 

 debated. There is a certain superficial likeness between Chagosia, Wlkr. 1909, and these 

 two genera. Walker placed his genus in the Calliopiidae provisionally, without examining 

 the mouth-parts, and until these are examined the genus has really only a nominal status. 



Cacao lacteus, Brnrd. (Fig. 90). 

 Barnard, 1931, p. 428. 

 Occurrence: St. 273. East mid-Atlantic. 8 3S 12-13 mm., 5 ovig. $? 14-15 mm., 6 immat. 

 9-10 mm. 



Description. Body plump, especially anteriorly. Integument not indurated. Back 

 rounded. Head longer than any of the peraeon segments, rounded in front, rostrum 

 minute; inferior margin of head rounded, anterior margin occupied by the very large, 

 subcircular, prominent eyes. Peraeon segment 1 equal to segment 2, the following 



