ISOPODA. 9 



improbable that a separate genus will be thought desirable for these species, when 

 they are more fully known. 



Gnathia insolita, n. sp. Plate XII. (B). 



The head is very broad, markedly emarginate between the mandibles, the minute 

 rostral point in the emargination only becoming visible after mounting, which 

 involved some flattening of the frontal border. The telson is acutely triangular. 

 Eyes small, dark, oval, slightly oblique in position, facets numerous. 



Upper antennas : Second joint shorter than first, first shorter than third, flagellum 

 with very short first joint, long second, which is subequal to remaining three joints 

 combined. 



Lower antennas : These are longer than the upper, with second joint of the four- 

 jointed peduncle much the shortest ; of the six-jointed flagellum the first joint is the 

 longest. 



The mandibles implanted wide apart are of uncommon pattern. There is no tooth 

 on the outer margin ; about midway on the inner is a quadrate process that might 

 represent the molar ; the apical part presents two strongly divergent teeth, with a 

 small convex lamina at the bottom of the cavity between them. 



The maxillipeds are of very delicate structure, except for the strong muscles in the 

 second joint. This joint is broader than long, not showing any distinct apical lobe. 

 In the four-jointed palp each joint is successively narrower than its predecessor. 

 They have the outer margin fringed with setae, 3 on the first, 5 on the second, 8 or 9 

 on the third, and 7 on the rounded incurved fourth joint. 



The first gnathopods are very distinctive of the species, not having the ordinary 

 tapering character, but the principal joint being as broad as it is long. Within are 

 seen the chitinized areas, probably indicative of original joints now in coalescence. 

 The middle area is the most extensive, the lowest has a feebly indicated companion. 

 The upper half of the rounded margin is furnished with 21 graduated setae. This 

 margin is the upper and inner when these valve-like limbs are closed together, but it 

 is not to be inferred that that is the proper description according to homology. There 

 is a very small apical joint, with no trace of a division into two joints. 



The second gnathopods are rather longer than the four pairs of peraeopods, of 

 which the second pair are slightly the shortest. In general character all five pairs of 

 trunk-limbs agree. 



The first pleopods have the rami rather longer than those of the other four pairs. 

 All five agree with the uropods in carrying rather long setae, which is contrary to 

 custom in the adult male of this genus. 



Length barely 2 millims., breadth a little less than half the length. 



Locality : Gulf of Manaar, off Karativo, from a sponge. 



The specific name refers to the unusual characters of the mandibles and first 

 gnathopods. 



C 



