TANAIDACEA AND ISOPODA— TATTERSALL. 245 



and none of them elongated ; side-plates well developed on all the free thoracic 

 somites, but those of the second thoracic somite not expanded to cover partially 

 the oral area; abdomen of two segments, but two further segments indicated 

 laterally by grooves ; first antenna relatively long and stout, with a regular series 

 of sensory filaments in pairs all along the lower margin of the fiagellum ; second 

 antenna not very long, rather stout, flagellum of two joints terminated by a 

 strong spine and not pectinate ; mouth-parts very similar to those of the genus 

 Arcturella, but I could not find any coupling hooks on the maxillipedes ; second 

 thoracic limb with the proximal part of the dactylus narrow and linear ; third to 

 fifth thoracic limbs with the fourth joint not specially elongate, dactylus distinct 

 though small ; sixth to eighth thoracic limbs not bi-unguiculate but having two 

 strong setae on the inner margin of the dactylus near the tip ; first pleopods 

 of the male modified, having a secondary lobe on the inside of the exopod. Type, 

 Pseudarcturella chiltoni, Tattersall. 



This interesting genus is distinguished from all the other genera of the Arcturidae 

 by the peculiar modification of the first pleopod of the male. I know of nothing quite 

 like it in other Isopoda, and it is a modification of quite a different order from that 

 found in the genus Antarcturus. 



Pseudarcturella approaches the genera Arcturus, Antarcturus and Nearcturus in 

 having the fourth free somite of the body not appreciably longer than any of the 

 other seo-ments. 



It differs from Arcturus in the reduced flagellum of the second antenna and in 

 the non-expansion of the side-plate of the second thoracic somite to cover the oral area. 

 In the last character it agrees with Antarcturus, but the latter agrees with Arcturus in 

 the form of the antennal flagellum. 



Pseudarcturella agrees with Neoarcturus in the characters of the segmentation of 

 the thorax, in the reduced flagellum of the antennae, and in the coxal plates of the 

 second thoracic segment ; but Nearcturus has four segments in the abdomen, is without 

 eyes, and the body is not geniculate, while the first pleopod of the male is not 

 modified. 



In the reduced flagellum of the antennae Pseudarcturella approaches the 

 Astacilla group of genera, and among this group it approaches the genus Arcturella in 

 the form of the second thoracic fimbs with their linear dactylus. But from this group 

 of genera it is at once distinguished by not having the fourth free somite of the thorax 

 elongated. Altogether the genus is a quite peculiar one, combining characters of the 

 Astacilla group with those of the Arcturus group and strongly marked off" from both 

 by the extraordinary form of the first pleopod of the male. 



50. Pseudarcturella chiltoni, sp. no v. PI. X, figs. 4-11. 



Occurrence. — Station 135, Spirits Bay, near North Cape, New Zealand, 3 metres, 

 tow-net at night, one male, 4 • 5 mm. 



