EEPOET ON THE ISOPODA. 29 



anterior segments of the body are much broader than the three succeeding segments, as 

 well as longer. The surface of the hody is quite smooth, with the exception of a transverse 

 ridge on each of the thoracic segments. 



The head is short and almost enclosed by the succeeding segment of the thorax ; its 

 dorsal surface, as of the body generally, is very convex, the anterior margin of the head is 

 rounded ; the antennules are lodged in a semicircular incision situated at the postero- 

 lateral extremity of the head. 



The four anterior segments of the thorax with the head are about as long as the three 

 posterior segments and the abdomen taken together. The first two segments are equal 

 in length and rather shorter than the third and fourth, which are themselves equal. The 

 width of these segments gradually increases up to the third ; the fourth segment is not 

 much narrower than the third. The lateral margins of the segments project as rounded 

 elevations ; in the second and third segments there is a straight marginal region behind 

 the rounded projection, which in the first and fourth segments occupies the whole of the 

 lateral margin. The epimera of these segments are prolonged into stout spiny processes ; 

 in the first segment the epimera are as well-developed as in the succeeding ones. 



The three posterior segments of the thorax are separated from each other and 

 from the fourth by deep lateral incisions ; their antero-posterior diameter is consider- 

 ably less than that of the preceding segments and they are also narrower ; their width 

 decreases regularly from the fifth to the seventh, but their length increases slightly. 

 On each of these segments, as on the four anterior, there is a median dorsal ridge 

 which ceases some way before the lateral margin of the segment ; the lateral margins of 

 the segments are rounded off, and the whole of the lateral regions are directed back- 

 wards, all three segments being approximately parallel. 



The epimera are more conspicuous on a dorsal view than those of the anterior 

 segments, as they project further outwards ; each is prolonged into a spine-like process over- 

 lying the articulation of the limbs, which is shorter in these segments than in the anterior. 



Between the last thoracic segment and the abdominal shield there is a single free 

 abdominal segment, which is separated by a distinct suture both from the seventh segment 

 of the thorax and from the abdominal shield ; it bears a median ridge like that upon the 

 preceding segments, but the lateral regions are not prolonged ; the segment is narrower 

 than the abdominal shield. The latter is divided into two regions by a notch at the 

 point where the uropoda are articulated ; the anterior region is nearly circular in outline ; 

 the posterior region is triangular and terminates in a sharp point ; the lateral margin of the 

 posterior region (fig. 12) is slightly serrated, the serrations becoming more marked towards 

 the apex, and fringed like the rest of the abdominal shield with a few slender hairs. 



The antennules (fig. 8) are of about half the length of the antennas. 



The peduncle consists of the usual four joints, but it is impossible, except by the 

 analogy of other Isopoda, to draw any line of demarcation between what ought to be 



