REPORT ON THE CRUSTACEA MACRURA. 441 



The next, which is the youngest known stage (PL LXXVIII. fig. 3), is in the Acan- 

 thosoma condition, and as such approaches others in its generic value. 



The carapace is short, or about half the length of the pleon. exclusive of the telson. 



The rostrum is long, slender, and fringed with teeth ; the lateral margin of the 

 carapace corresponding with the antero-lateral angle is armed with a tooth of extreme 

 tenuity and fringed with small spines. 



Pleon armed with ornate spines or teeth on the lateral margins, and dorsally on the 

 posterior four somites. 



Telson (fig. 3z) bifurcate and terminating in two uniarticulate appendages, tipped with 

 one or two small hairs. 



The ophthalmopoda are large, broad, and fungiform. 



The first pair of antennas has a three-jointed peduncle, of which the first joint is 

 long and the two succeeding short, supporting two flagella, one short and uniarticulate, 

 the other scarcely half the length of the peduncle and Particulate. The basal extremity 

 of the first joint is not enlarged to receive an otolith. 



Second pair of antennas carries a flagellum that reaches but little beyond the 

 ophthalmopod, and a scaphocerite that nearly equals it in length, and which is furnished 

 on the outer margin, near the extremity, with a long tooth fringed with marginal teeth 

 (not properly represented in the figure). 



There are seven pairs of appendages that represent the gnathopoda and five pairs of 

 pereiopoda, of which the last two are feeble and the others tolerably robust. 



The pleopoda are all single-branched, and exhibit no signs of an inner ramus, except 

 the posterior pair, which goes to form the rhipidura. The plates of this pair are long, 

 narrow, and reach beyond the extremity of the telson ; the outer is armed with a strong 

 tooth one-third distant from the extremity. 



Length, 3 mm. (0"12 in.). 



Habitat. — North Pacific Ocean. 



Observations. — This is a younger form and may develop into either Sergestes or Acetes, 

 as it possesses no feature that might not become modified in the course of its progressive 

 growth. 



Acetes, Milne-Edwards. 



Acetes, Milne-Edwards, Ann. d. Sci. Nat., t. six. p. 350, 1830. 

 „ „ Hist. Nat. des Crust., t. ii. p. 429. 



There is no specimen in the extensive collection of species of this family that I can 

 recognise as belonging to this genus. 



Professor Brooks 1 figures a specimen as a young Acetes, jf^tli of an inch long 



1 Phil. Tram., pi. x. fig. 85, 1882. 



(ZOOL. CHALL. EXP. PAET LII. 1887.) Fff 56 



