REPORT ON THE CRUSTACEA MACRURA. 371 



Length, 2"5 mm. (O'l in.). 



Habitat. — The Western Pacific Ocean. 



Observations. — It is interesting to notice that this specimen, while only about two- 

 thirds the length of those from which figs. 1 and 3, PI. LXIV., were taken, yet has the 

 appendages parallel with them in development. 



Acanthosoma longitelsonis (PI. LXIV. fig. 3). 



The carapace is more than one-third the length of the animal including the telson - y 

 excluding the telson it is nearly one-half. 



The rostrum is about as long as the carapace, and fringed from base to apex with 

 small teeth ; a long and slender serrate spine projects above the ophthalmic notch ; a 

 short, curved, serrate process stands at the antero-lateral angle of the carapace ; a 

 little way behind it on the margin there is a long, slender, smooth spine, and a little 

 more posteriorly is another process or smooth tooth, broad at the base, short, and sharp- 

 pointed ; the postero-lateral and posterior margins are smooth. 



The pleon has the five anterior somites subequal, and dorsally armed with long 

 serrate spines, which project from the posterior margin and increase in length from the 

 first to the fifth somite ; each somite is likewise armed on each side at the postero-lateral 

 angle with long, slender, serrate spines that increase posteriorly to the fifth somite. 

 The sixth somite is about as long as the two preceding ones, it is dorsally smooth and 

 unarmed, except at the postero-lateral angles, which are produced into long, slender, 

 serrate spines, but not so long as those on the fifth somite. 



The telson is long, quite as long as the sixth somite, posteriorly forked, the limbs of 

 the fork being parallel at first and then slightly divergent, and armed on each side with 

 one strong posteriorly-directed tooth, and distally with several small teeth. 



The ophthalmopoda, about one-third the length of the rostrum or carapace, are slightly 

 fungiform, gradually increasing from the base and suddenly enlarging at the ophthaknus. 



The first pair of antennae has the peduncle three-jointed, and reaching to about half 

 the length of the rostrum ; the first joint is longest, the second and third subequal, and 

 the first joint is smooth excepting for two ciliated hairs on the inner and one on the 

 outer distal angle ; the second joint has two or three ciliated hairs on the inner and two 

 on the outer margin, and the third joint has two or three ciliated hairs on the inner 

 margin only ; attached to the distal extremity are two short branches, the outer repre- 

 senting the long and permanent flagelluni, and the inner and shorter the future small 

 and rudimentary appendage. 



The second pair of antennas has a stout basal joint that supports a long, slender 

 flagelluni,. apparently not multiarticulate, and a long and narrow scaphocerite that is 



