REPORT ON THE ISOPODA. 39 



overlaps the succeeding segment and recalls Serolis minuta, in which species (see below 

 p. 77) all those prominences are highly developed and project backwards as flat conical 

 processes over the following segments. 



The presence of a distinct lateral tooth below the termination of the carinse does 

 seem to distinguish Serolis plana from Serolis convexa where there is no such tooth, but 

 it would not be safe, I think, for the present to separate the two until a larger number of 

 specimens of both have been examined. 



In all the three species — Serolis gaiidichaudii, Serolis convexa, and Serolis plana — 

 the epimera of the second, third, and fourth pairs only are separated from the terga by 

 a distinct suture ; in the first two species the anterior epimera are divided by a 

 transverse suture as in so many other species ; this suture is, however, not very well 

 marked, and in the specimen of Serolis convexa obtained by the Challenger I could not 

 detect an 3^ trace of it, though it was distinctly visible in the British Museum specimens. 



Appiendages. — I give here a somewhat full description of the appendages which have 

 not been described by Cunningham. 



Antennce. — The posterior pair of antennte are decidedly longer than the anterior pair, 

 reaching as far as the end of the first epimera. 



Of the anterior pair, the first joint is somewhat broad and quadrangular, the second 

 joint is narrower and a little longer ; the anterior and posterior surface of both are covered 

 by a few scattered hairs ; the third joint is a cylindrical rod somewhat bow-shaped, and 

 only slightly longer than the preceding joint ; the fourth joint is short, about one quarter 

 as long as the third. The filament appear to consist of about twenty-five joints, and 

 each joint has two sensory hairs, one situated near the anterior extremity of the joint, the 

 other near its posterior extremity. 



The posterior i^air of antennae consist as usual of five joints and a filament. 



The first joint is the shortest, the second a little longer and somewhat hour-glass 

 shaped. The third, as usual, inserted in a wedge-like fashion between the second and 

 the fourth ; the fourth joint is the longest of the whole appendage, is somewhat bent, and a 

 ridge parallel with the curved lower margin runs along its whole length ; the joint narrows 

 towards its extremity, where it articulates with the terminal joint, which is a little shorter 

 and more uniformly cylindrical in shape ; the upper margin of the two last joints is 

 furnished with scattered tufts of hairs. The filament has twenty-one joints, which 

 increase in length but diminish in thickness towards its extremity. 



The mandibles have the cutting edge prolonged posteriorly into two subequal 

 conical teeth ; on the upper side are two spines situated one behind the other, the 

 anterior one rather longer and broader. 



Thejii'st maxillcB are in no way remarkable. 



The second maxillce (PI. VI. fig. 14) differ from those of most other species in that the 

 two anterior lobes are not much smaller than the posterior, and are furnished on the outer 



