Chilton. — On an Isopod inhabiting Ants^ Nests in New Zealand. 191 



unsuccessful, and at that time I could merely note tlieir occurrence in ants' 

 nests. In 1902 Mr. J. MacMalion sent me numerous specimens of an isopod 

 found in association with the nests of ants in the Kai Valley, in Marl- 

 borough, and later on Mr. Smith sent me similar specimens from New Ply- 

 mouth. Although these specimens were undoubtedly associated with the 

 ants, it was not quite certain that they were habitual guests in the nests, and 

 I therefore waited for further evidence. Recently, however, Mr. Smith 

 has found other specimens undoubtedly living in the ants' nests,* and 

 associated with two species of ants — viz., Ambhjopone cepkolotes, Smith, 

 and Huheria striata. Smith ; and I am therefore now able to describe the 

 isopod. It proves to belong not to Platyarthrus, but to Trichoniscus ; it 

 thus belongs to a different family of terrestrial isopods, and it is interesting 

 to note that we have here the same habit of life arising independently in 

 two quite different isopods. It is rather larger than Platyarthrus hoffmann- 

 seggii, being about 5 mm. in length, and, though very much lighter in 

 colour than the ordinary terrestrial Isopoda, it is not quite white, but is 

 generally marked with bands or patches of pale brown on a white ground. 

 Moreover, it is not blind, bvit possesses fairly perfect eyes, provided with, 

 apparently, the normal amount of pigment. The description of the species 

 is given below. 



Trichoniscus commensalis, sp. nov. 



Body rather broadly oval, fairly convex, pleon not abruptly narrower 

 than the peraeon ; whole dorsal surface thickly covered with spiny tubercles, 

 which are arranged more or less regularly in transverse rows — viz., one row 

 along the posterior margin of each segment, and two or three much more 

 irregular rows on the anterior part of each segment. In the pleon there 

 is a fairly well-marked row along the posterior margin of the third segment, 

 the other portions of the dorsal surface of the pleon usually bearing only 

 minute spines. 



First segment of perseon the longest, and produced into two roimded 

 lobes reaching as far as the eyes ; the last segment of the peraeon with the 

 postero-lateral angles produced so as to include the first three segments 

 of the pleon, and to reach almost to the end of the epimera of the 3rd seg- 

 ment ; in the pleon the 3rd, 4th, and 5th segments bear fairly well-developed 

 epimeral portions. Terminal segment with the sides concave, the angles 

 rounded, posterior margin straight or very slightly convex and bearing 

 four small spines. 



Eyes fairly well pigmented, formed of three ocelli, fairly close together. 



Antennfe stout, especially the penultimate segment of the peduncle, 

 which is half as broad as long, the last segment longer than the preceding, 

 and bearing fine setae on the outer side and roughened tubercles on the 

 inner ; the flagellum as long as the last segment of the peduncle, composed 

 of five joints, the last bearing a pencil of fine hairs. The uropoda fairly 

 stout, outer branch stouter but not much longer than the inner, both 

 covered with fine setae and bearing a tuft of longer setae at the extremity. 

 In the last pair of legs the ischium is produced on the outer side into a 

 prominent triangular process or plate bearing one or two stout setae. 



Colour white with pale-brown markings, usually more or less arranged 

 in longitudinal lines ; the colour, however, varies very considerably, some 



* Ml'. Smith says that on one occasion " the ants were in the act of carrying off the 

 specimens when I took them from them." 



