1480 THE VOYAGE OF H.M.S. CHALLENGER. 



part only of that margin pectinate and not strongly, the inner margin only slightly 

 serrate ; the second pair as in Paratyphis promontorii ; the third pair with the outer 

 ramus less than half the breadth, but a little more than half the length of the inner, 

 the maro-ins of each being very minutely pectinate ; the inner ramus reaches a little 

 beyond the telson. 



The Telson as in the species just mentioned, but with much narrower apex, the 

 sides straighter and converging more rapidly. 



Length, less than a fifth of an inch. 



Locality.— August 24, 1875; 400 miles south of Hawai; lat. 13° l'N.,long. 151° 50' W.; 

 surface at night; surface temperature, 78 0- 2. 



Remark. — The specific name refers to the capture of the species in the Mid Pacific 

 Ocean. From Paratyphis parvus, Glaus, it is distinguished by the produced apex of the 

 third joint in the fourth perseopods, the two- to three-jointed fifth peraeopods, and the 

 longer outer ramus of the third uropods, but the species bear a close resemblance to 

 one another. 



Genus Tetrathyrus, Glaus, 1879. 



1879. Tetrathyrus, Glaus, Die Gattungen und Arten der Platysceliden, pp. 4, 14. 



1886. ,, Gerstaecker, Bronn's Klassen und Ordnungen, Bd. v. Abth. ii. p. 483. 



1887. „ Bovallius, Systematical List of Amph. Hyper., Bihang. till K. Svensk. 



Vetensk.-Akad. Handl., Bd. 11, No. 16, p. 47. 

 1887. ,, Glaus, Die Platysceliden, pp. 31, 40. 



For the definition in the original language, see Note on Claus, 1879 (p. 491). 



In the preliminary table of the family Typhidse, Claus gives as the character common 

 to Tetrathyrus and Amphithyrus : — 



" Both pairs of gnathopods subchelate. The two terminal joints of the hinder 

 antennae in the male as long or nearly as long as the preceding." 



To distinguish Tetrathyrus from the companion genus he gives the characters : — 



" Gnathopods simply subchelate. Laminar first joint of the fourth perceopods without 

 pocket-shaped groove." 



Tetrathyrus moncceuri, n. sp. (PL GLXXXIV.). 



Dorsal surface of the head with a downward slope, the rostral triangle bent in and 

 tip-tilted ; the back broadly rounded ; first two segments of the peraaon very short 

 dorsally, especially the second ; the first three segments of the pleon conspicuously 

 larger than any of the peraeon-segments. 



