112 
THE VOYAGE OF H.M.S. CHALLENGER. 
also in tlie great length 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 mgny 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 1^^ 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 shown in PI. VI. figs. 2 and 6, and PL 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 
f-^ 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 the 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. 
