REPORT ON THE CRUSTACEA MACK I IRA. 513 



articulate ; the propodos is very short and scarcely broader than the carpos, the inferior 

 distal angle is produced to a sharp polliciform process, against which the small sharp 

 dactylos impinges obliquely. 



The three posterior pairs of pereiopoda are strong, slender, well-formed, simple 

 appendages. The coxa is short and large, the basis short and narrow and with the outer 

 side oblique, and it articulates with the ischium, which is moderately long and slender, 

 and has the distal extremity oblique and articulating with a long slender meros, the 

 extremity of which slightly increases in size and articulates with the carpos, which just 

 beyond the joint suddenly curves at nearly a right angle ; it is about half the length of 

 the meros and cylindrical ; the propodos is cylindrical, one-third longer than the meros, 

 and distally furnished with hairs, amidst which a cylindrical dactylos articulates and 

 terminates in a narrow, sharp pointed unguis. 



The first pair of pleopoda ( Z p ¥ ) articulates with the coxal plate on the inner side, 

 nearly at the extremity, opposite to an external boss or large tubercle ; the basis is long, 

 pedicular, and supports two fobaceous plates, of which the inner and posterior is the 

 smaller and carries attached to the inner margin a small stylamblys, furnished towards 

 the extremity with small, obtusely pointed cincinnuli. The four following ]:>airs of 

 pleopoda ( $ q $ ) are formed upon the same type as the first, but the fobaceous branches 

 are larger and the inner one in the male supports two of the small stylamblydes, one of 

 which is fringed with hairs. 



The posterior pair of pleopoda, which helps to form the rhipidura, has the basal joint 

 short and the fobaceous plates long. The inner plate is pointed and fringed with hairs, 

 the outer rounded, having a diaeresis near the external marginal tooth, from which point 

 it is fringed with hairs along the distal and inner margins. 



The telson is long, narrow, and tapering; it is rudely quadrate in transverse sect i mi 

 at the anterior extremity, and cylindrical at the apex; the angles are longitudinally ridged, 

 those on the upper margin being slightly serrate, and the dorsal surface is depressed or 

 grooved but furnished in front with a strong pointed cusp in the median line, which 

 represents the terminal continuation of the dorsal carina of the pleon, with wdiich, when 

 the animal is extended, it is in close apposition. 



The animal during life has the power of locking the telson in a fixed position, when 

 undoubtedly it becomes a very powerful weapon of offence, and again unlocking it at its 

 own will. The male and female closely resemble one another, but the female is larger 

 than the male ; all the parts in the two sexes have a similar proportional relation except 

 such as may be supposed to be sexually variable. 



The first pair of antennas in the male has the external or primary flagellum broader 

 and more thickly studded with membranous cilia ; like the ophthalmopoda these antennae 

 stand upon a rudimentary ventral arc of the first somite. The acoustic organs appear to 

 be internally well developed and occupy a chamber in the first joint. The upper surface 



(ZOOL. CHALL. EXP. PART LII. 1887.) Fff 65 



