96 
THE YOYAGE OF H.M.S. CHALLENGER. 
which, starting with Alima gracilis, with its short carapace and elongated hind body, 
leads, through many intermediate types, to a larva which is short and wide, and 
almost completely covered by the elongated carapace, like an Ericlithus, although its 
general structure is Alima-\\ke,. For this larva, which he justly regards as the ancestral 
form from which the Alima larvae have been produced, Claus proposes the provisional 
generic name Alimerichthus, as expressing its double relationship, to Alima on the one 
hand, and Erichthus on the other. 
He figures 1 a single advanced larva of this type 18 mm. long from the Indian Ocean, 
but as he gives no account of its early stages, the occurrence in the Challenger collection 
of younger specimens of this type is a matter of great interest, as these younger larvae 
show that the young Alimerichthus, like the young Alima, passes through a stage in 
which the last six thoracic somites have no appendages, while the raptorial limbs of the 
second thoracic somite and the first pairs of abdominal appendages are well developed 
and essentially like those of the adult. 
I have selected from a collection made, February 29, 1886, in the South Atlantic, off 
the coast of South America, in lat. 36° 9' 8" S., long. 48° 22' W., the two specimens 
which are shown in PI. VIII. fig. 8, and PI. IX. fig. 3, and which represent a form 
which is very closely related to, but probably not identical with the one figured by 
Claus. The youngest, shown in PL VIII. fig. 8, is 8 71 5 mm. long, and the next stage, 
shown in PI. IX. fig. 3, is 15 - 52 mm. long, while Claus’s Alimerichthus is 18 mm. 
long, so that we probably have, in this series, three successive moults in the history 
of the larva for which Claus’s generic name may be retained without a specific 
name. Alimerichthus is characterised as follows — A short wide Alima with a short 
hind body which is wide and flat in the older larvae. The mouth is near the middle of 
the carapace, and the rostrum is less than half as long as the carapace, which has a 
median dorsal spine, and moderately long antero- and postero-laterals. There is a second- 
ary spine on the inner edge of the postero-lateral close to its base, and a very prominent 
acute spine projecting outwards from the lateral edge of the carapace, about midway 
between the bases of the antero- and postero-lateral spines, and two or three smaller ones 
projecting inwards between this and the one at the base of the postero-lateral. The 
length of the carapace, measured on the middle line, from the tip of the rostrum, makes 
much more than half the total length, and it covers all of the thorax except the tip of 
the eighth somite, while the tips of the postero-lateral spines are in the line of the 
anterior edge of the telson. The eye stalks are about as long as the eyes, which have 
swollen globular tips, the width of the carapace equals about one-third the total length, 
the telson is wider than long, with six marginal spines, and numerous secondary spines 
between the submedians and also between each submedian and the adjacent intermediate. 
The inner spine of the basal prolongation of the uropod is slightly longer than the outer, 
1 Metamorphose der Squilliden, p. 147, Taf. viii. fig. 30. 
