206 Transactions. — Zoology. 



ISOPODA NOEMALIA. 



Fam. AECTUEIDiE. 

 Genus Arcturus, Latreille. 



Body slender and cylindrical, fourth segment greatly elongated. Antero- 

 lateral margins of the head produced forward. Eyes large, semi-globose. 

 Superior antennas very short. Inferior antennae long. Four anterior pairs 

 of legs slender and ciliated ; abdominal legs short and very robust. 

 Terminal segment of abdomen large, scutiform, and furnished below with 

 two large opercular plates (somewhat similar to Idotea.) 

 1. A. tuberculatus, G. M. Thomson (Ann. & Mag. N.H., ser. V., vol. IV., p. 416). 



Fig. 2. 



Male. — Body rather robust. Head very indistinctly separated h'om first 

 thoracic segment, and together with the two succeeding segments pro- 

 duced upwards into acute tubercles. Fourth segment smooth, bearing a 

 single stout spine at each extremity, the posterior one behig bifid. Superior 

 antennae reaching beyond extremity of second joint of inferior ; basal joint 

 stout, second and third short, fourth as long as the two preceding, and 

 bearing several articulated processes, consistmg each of a basal joint, and a 

 long lamellar appendage. (From want of sufficient specimens, I have not 

 been able to investigate the function of these appendages). Inferior 

 antennae rather longer than four anterior segments of the body, not 

 ciliated, but with rows of minute tubercles on the lower margin ; first and 

 second joints rather short ; third and fourth long ; flagellum three-jointed, 

 finely serrated on its inner margin, and furnished with a few cilia. The 

 inferior antennae are the chief organs of progression in the animals of this 

 genus, and also serve to catch the prey and bring it to the mouth ; in this 

 species they are apparently well-fitted for their functions. 



The fetnale differs from the above in having the whole body (except the 

 margins of the lower antennae) more or less tuberculate. The head and three 

 posterior segments bear a row of tubercles on each side. The fourth seg- 

 ment is flattened on its posterior lateral margins ; it bears on the median 

 line at its anterior extremity a large three-pointed tubercle, behind which 

 are three smaller tubercles placed transversely, the middle one being the 

 smallest ; on each side of the anterior margin are two tubercles, the lower 

 of which is the largest. The oviferous pouch extends along three-fourths 

 of the lower surface of this segment. The fifth segment of the body is ex- 

 tended downwards as if to form a supplementary pouch. 



Length -2 inch, exclusive of the inferior antennae. 



Hab. Dredged in Dunedin harbour, 4-5 fathoms. 



(This may be Leachia nodosa, Dana.) 



