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



also in the great leugth of the narrow hind body. His collection contained numerous 

 specimens, all very similar in general appearance to the one which he traced to its adult 

 form, from various localities in the Indian and Atlantic Oceans. They are all narrow 

 and elongated and from 16 to 42 mm. long. 



The Challenger collection also contains numerous specimens from many widely 

 separated localities ; all so similar to the one which Claus studied that they must 

 pertain to closely related adults, and I therefore place them all in a provisional genus 

 Pseuderichthus. One of them I^^q inches long, from a collection made between 

 Tenerife and St. Thomas, is shown in dorsal view in PI. XII. fig. 6, while various parts 

 of its body, more highly magnified, are showni in PI. VI. figs. 2 and 6, and PI. XIII. 

 figs. 12 and 14. The telson and uropods of a very similar but much larger specimen, 

 If inches long, from Volcano, are shown in PI. VI. fig. 7. Another much smaller 

 species, which undoubtedly belongs in the same group, although it is much wider and 

 flatter than the one figured above, is shown in side view in PI. V. fig. 4. It is 

 |-J inches long, and is from a gathering made between Api and Cape York. In all the 

 older larvae of this group the submedian spines of the telson are very long and slender, 

 and are tipped with movable spinules, as in the adult Pseudosquilla ; the proximal 

 joint of the exopodite of the uropod is bordered by numerous (six to twelve) spines, the 

 terminals are much longer than tlie others, and the dactylus of the raptorial claw often 

 exhibits traces of two or three marginal spines under the cuticle. As all these 

 characteristics are features of resemblance to the adult Pseudosquilla, and as Claus has 

 obtained a very complete series of stages connecting one of these larvae with an adult 

 of this genus, there can be little doubt that they are all Pseudosquilla larvae. 



While it is very closely related to both Lysioerichthus and the Erichthus of Gono- 

 dactylus, and united to both these larval types by intermediate larval forms, I believe 

 the following features may be relied upon as diagnostic of the Pseuderichthus larva. It 

 is distinguished from the Lysioerichthus by the position of the postero-lateral spines of 

 the carapace, which are near the dorsal surface ; by the narrowness of the carapace, 

 which is at least twice as long as wide, shallower than in Lysioerichthus, and not at all, 

 or only very slightly, infolded along its lateral edges ; by the elongation of the hind 

 body, the length of the submedian spines of the telson, the presence of numerous spines 

 on the outer edge of the proximal joint of the exopodite of the uropod, and the very 

 great elongation of the outer one of the two ventral spines on its basal joint. It is 

 distinguished from the Erichthus of Gonodactylus by the fact that the postero-lateral 

 spines of the carapace are short, usually only one-fourth or one-third as long as the 

 carapace, while they are usually more than half as long in the Gonodactylus larva, and 

 also by the fact that the rostrum is usually short and compressed, and armed at about 

 the middle of its ventral edge by a large acute curved spine, in front of which there are 

 often two or three smaller spines. 



