REPORT ON THE CRUSTACEA MA CRURA. 427 



The sixth somite is as long as the three preceding combined, and is armed dorsally 

 on the posterior margin with a horizontal tooth and with a small tooth at the postero- 

 lateral angles, while the median ventral lobe is unarmed and reduced in size, and has 

 the nerve-ganglion belonging to this somite lodged in it. 



Telson about one third the length of the sixth somite, deep at the antero-lateral 

 margin and narrow at the distal extremity, where it is armed with two sharp teeth. 



Ophthalrnopoda fungiform (fig. 5a), and nearly four times longer than the rostrum. 



First pair of antennae having the first joint of the peduncle a little shorter than the 

 ophthalrnopoda ; the second joint about one third the length of the first, and the third 

 about half the length of the second. 



The second pair of antennae has the last joint of the peduncle reaching to one third 

 the length of the ophthalmopod, and the scaphocerite,- which is narrow, with the margins 

 parallel, and armed near the extremity with a sharp tooth, reaches as far as the distal 

 extremity of the peduncle of the first pair of antennae. 



The epistoma is largely developed and projects anteriorly to near the posterior 

 extremity of the antennae. 



The mandibles are strong, but I cannot detect a synaphipod attached. 



The first pair of gnathopoda is similar to that in other species. 



The second pair. is attached to a large coxa and is robust as far as the fourth joint, 

 the distal two being slender and fringed with hairs, and subequal in length with the 

 animal. 



The first pair of pereiopoda is short, slender, and is not furnished with a small 

 tubercle on the anterior margin of the ischium. The second pair of pereiopoda is 

 long and slender, and has the ischium furnished with a small tubercle. This pair 

 terminates in a rudimentary or scarcely determinable chela furnished with long hairs. 

 The third pair resembles the second in length and proportion, but has the ischium 

 smooth and the terminal extremity without a trace of a chela, and is furnished with 

 long hairs. 



The fourth and fifth pairs are apparently missing. 



The pleopoda are slender and decrease in length posteriorly. 



The sixth pair, which forms the outer plates of the rhipidura, is long, narrow 

 and pointed ; the outer plate is longer than the inner, and nearly four times the length 

 of the telson, it has no tooth on the lateral margin, and is slightly curved, and fringed 

 with hairs that increase in length posteriorly. 



Length, 35 mm. (0 - 14 in.). 



Habitat. — North Pacific Ocean. 



This species should be compared with Mastigopus spiniventralis (p. 379 ; PI. LXVII. 

 fig. 4), the specimen of which, with three others on the same slide, is labelled by Dr. v. 



