REPORT ON THE CRUSTACEA MACRURA. 385 



has acquired specific features, but is not yet maturely developed, since the dactyli of 

 the second and third pairs of pereiopoda are shorter than the pollex, as if these minute 

 chela; were not yet fully developed ; a condition that is also apparent in the incipient 

 stage of the two posterior pairs of pereiopoda, and in the immature condition of the inner 

 ramus of the pleopoda. 



It is highly probable that this species is a more advanced form in the development of 

 that of which Mastigopus spiniventralis is but a younger stage. 



Sergestes prehensilis, Spence Bate (PL LXXL). 



Sergestes prehensile, Sp. B., Ann. and Mag. Nat. Hist., ser. 5, voL viii. p. 193, 1881. 



Carapace about one-fourth the length of the animal, slender and smooth, armed 

 in front with a short, sharply-pointed rostrum, directed obliquely upwards. Pleon 

 smooth. Telson half the length of the outer ramus of the rhipidura. 



Ophthalmopod (a) about twice the length of the rostrum, without a tooth or tubercle 

 on the side. Ophthalmus large, in breadth equal to half the length of the ophthalmopod. 



The first pah- of antenna? (b) has the peduncle three times as long as the ojihthalmopod ; 

 the first joint is flattened and centrally hollowed, without a prosartema, which is repre- 

 sented by a tuft of hairs, and the stylocerite is short, stout, and terminates in a sharp 

 tooth ; the two succeeding joints are nearly as long as the first, cylindrical, and 

 terminate in two flagella, one of which is extremely long, and has a small multiarticulate 

 enlargement at its base supporting slender, flexible cilia ; the second is short, slender, 

 and feeble, being a little longer than the terminal joint of the peduncle. 



The second pair of antennae has the scaphocerite nearly as long as the peduncle of 

 the first pair, and has the external tooth in a line with the distal extremity. The 

 phymacerite exists as a small tubercle, directed forwards and upwards, and the ancecerite 

 on the upper surface is curved and pear-shaped. 



The mandibles (d) have sharp and even psalisiform margins, and carry a long, slender, 

 two-jointed synaphipod ; behind them are two long bat-shaped metastomata, which 

 overlie the mandibles, and the margins meet the cheiloglossa in front. 



The first pair of siagnopoda (e) is three-branched, and resembles that of Benthesicymus 

 and Gennadas. 



The second pair (/) is three-branched, and carries a broad mastigobranchial plate 

 that projects anteriorly as far forwards as the extremity of the second foliaceous branch. 



The third pair (g) is three-branched ; the first or coxa is short, and carries a long 

 mastigobranchial plate ; the second is foliaceous, and armed on the inner side with 

 long serrate spines ; the third consists of three joints articulating in succession, the basal 

 being armed with two large and several small spines, and carrying on the outer side a 

 long narrow, membranous plate. 



(ZOOI.. CilALL. EXP. — part lti. — 188G.) Fff 49 



