58 THE VOYAGE OP H.M.S. CHALLENGER. 



Ibaccus verdi, n. sp. (PI. VII. fig. 2 ; PL VIII.). 



This species bears a general resemblance to Ibaccus incisus (Peron) (Ibaccus peronii, 

 Leach), but has the lateral margins of the carapace armed with seventeen teeth posterior to 

 the cervical notch, and two small teeth on the angular cusp anterior to it. There are six 

 teeth along the lateral margin of the third antenna! joint, which does not slope inwardly 

 so much as in Ibaccus incisus. The terminal scale has the distal margin fringed with 

 nine strong short teeth in the female. In most other important points this species 

 nearly resembles Ibaccus incisus. 



The male differs from the female in having the distal margin of the terminal scale of 

 the second antennae smooth or slightly wavy, and in having the posterior pair of perei- 

 opoda terminating in a sharp pointed lanceolate dactylos (PI. VIII. fig. o, $ ), whereas in 

 the female the dactylos is short (fig. o, ¥ ), and impinges against a short and robust pollex, 

 entirely wanting in the male. 



The pleopoda also differ very much in the two sexes. 



In the male none are attached to the anterior somite, but the four succeeding have a 

 pair each, successively diminishing posteriorly (PL VIII. figs, jg and q, $ ). They consist 

 of two branches, flat, narrow, curved, and pointed, the outer branch being sharper than 

 the inner, and more distinctly defined in the posterior than in the anterior pairs. The 

 branches are not on the same line, but the inner articulates at the apex, and the outer 

 laterally with the basal joint. The margins of both branches are fringed with numerous 

 hairs that are longer and more abundant on the anterior pairs than on the posterior. 



The female, like the male, has no appendage attached to the first somite of the pleon; 

 the second (PL VIII. fig. q, $ ) bears a pair of large two-branched foliaceous plates, 

 standing on small stalks. The three following pairs are likewise two-branched, but the 

 outer branch is small and foliaceous, articulating with the stem near its base, whereas the 

 inner is three-jointed, long, narrow, stiff, and articulates with the stem at the extremity, 

 except for the slight squamose extension at its base. These are fringed with very long 

 hairs, much longer than shown in the plate. 



Habitat— St. Vincent, Cape Verde Islands, July 1873, depth 7 to 20 fathoms. 

 Length, 1 130 mm. (5"25 inches). 



Station 200, off Samboangan, Philippine Islands, October 23, 1874; lat, 6° 47' N., 

 long. 122° 28' E. ; depth, 250 fathoms; green mud. Length, 114 mm. (4 '25 inches). 



Although several species of this genus have long been known, it will not be without 

 considerable advantage to analyse the structure of the various parts, in order to enable us 

 to compare them with their homologues, in forms that are thought to be more or less 

 congeneric. 



1 In measuring the Scyllaridse, I have taken the length from the extremity of the larger antenna? to that of the telson. 



