REPORT ON THE ISOPODA. 173 



Macrostylis, Sars. 

 Macrostylis, Sars, ForhandL Vidensk. Selsk., 1863. 



A single specimen, dredged in 2050 fathoms at Station 246, appears to be referable 

 to this genus, which is defined by Sars as follows : — 



"Body narrow, tapering posteriorly. Head large, the frontal margin projecting 

 between the antennae. Antennules also very short, antennae long, the flagellum shorter 

 than the base. Mandibular palp absent. The two first thoracic segments short ; the third 

 much larger; the fourth with pointed lateral processes; the fifth, sixth, and seventh 

 segments of equal size, separated by deep lateral incisions and with pointed lateral processes. 

 The two first pairs of ambulatory limbs short, with a strong terminal claw ; the third larger 

 and very powerful, with the joints expanded and furnished with numerous spines; the 

 fourth pair again small and slender; the fifth to the seventh pairs with the joints hardly 

 dilated, increasing progressively in length. Abdomen large, swollen in the middle, 

 terminating in a blunt extremity. Uropoda long and slender, simple, two-jointed, the 

 terminal joint short. 



The occurrence of this genus in very deep water is another instance of the range of 

 Arctic littoral genera into deep water (see p. 159). 



Macrostylis latifrons, n. sp. (woodcut, fig. 2). 



The single specimen of this species measures 5 mm. in length. The shape is 

 cylindrical, slightly wider at the anterior than at the posterior extremity. 



The head is separated from the first thoracic segment by a very marked constriction ; 

 in general shape it is semicircular, the anterior margin being convex, the posterior straight. 

 The postero-lateral angles are very sharp. 



The thorax consists of the usual seven free segments; of these the first three are so 

 closely united together that they appear on a superficial examination to be absolutely 

 fused ; this, however, is not the case. The first two segments are subequal, with concave 

 anterior and convex posterior border; the anterior border is exactly parallel to the 

 posterior in both segments ; the lateral margin of the segments is perfectly straight, 

 parallel to the long axis of the body, and there is hardly any notch between the successive 

 segments. The third thoracic segment is larger than either of the foregoing ; its concave 

 anterior border follows closely the convex posterior border of the segment in front; the 

 posterior border of the third segment is straight. 



The fourth segment of the thorax is separated from the third by a deep lateral notch, 

 as are also the remaining segments from each other. The fourth segment is rather 

 shorter than any of the succeeding, but a little longer than either of the two first; its 

 anterior and posterior margins are approximately straight and parallel to each other. 



