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



the lower Lysiosquillai, in the subgenus Coronis, the larva is not an Alima 

 but a Squillerichthus, and if it be true that Squilla and Lysiosqidlla represent two 

 divergent stems, and that their lower representatives are most closely related, it is 

 not at all jirobable that any species of Lysiosquilla passes through an Alima stage, for 

 if it were the case we should be forced to beheve that the higher Lysiosquillee have inde- 

 pendently acquired the same secondary larval form as the higher Squillae. 



While Glaus has given us a very complete history of the Erichthus larva his 

 collections did not furnish a connected series of Alima larvae, and although he points out 

 the possibility tliat the very young larva which had been figured by Fritz Midler,^ as well 

 as a very similar one from Messina which he himself figures,^ are young Alima3, he was 

 unable to obtain any of the intermediate stages, and my paper on the larval stages of 

 Squilla empusa is the only one in which a tolerably complete series of Alima larvae 

 are figured. In this paper I showed that the distinctive characteristics of the larva are 

 present at a very early stage of development, and that it is in all essential respects an 

 Alima at a time when the last three thoracic somites are not yet marked out, and when 

 there are no appendages between the large raptorial limbs of the second thoracic somite 

 and the first abdominal appendages. I also pointed out the great probability that this 

 larva leaves the egg as an Alima rather than as an Erichthoidina or an Erichthus; a 

 probability which is strengthened by the fact that Fritz Miiller has figured an egg con- 

 taining a larva which is probably in this stage. 



Squilla {Alima) gracilis. — The Challenger collection contains a number of larvae 

 which were collected in the tow-net at St. Vincent, and from these I have been able to 

 select a series of Alimse, which give a much more complete history of the growth 

 and gradual modification of the larva than that which I obtained in 1879. 



This series of larvae, Alima gracilis of Milne-Edwards {Alima angustata, Dana) is 

 shown in PL IV. figs. 4-6, PL V. fig. 3, PL VI. figs. 3-5, and PL VIII. figs. 4-6. 



Its distinctive or specific characteristics are as follows : — The body is narrow and 

 greatly elongated, the exposed hind body making about half the total length as 

 measured from the tip of the long slender rostrum. The raptorial claw of the second 

 thoracic appendage (PL VIII. fig. 5) is narrow and greatly elongated, and the dactylus is 

 only about half as long as the second joint. 



The telson is remarkably long and narrow, and in the older larvae its length is three 

 times its width. It has six large marginal spines (PL VI. fig. 3 and PL VIII. fig. 6) with 

 minute spinules between the submedians, and also between the submedian and the inter- 

 mediate. The lateral edge of the greatly elongated narrow flat carapace is armed with 

 twelve or thirteen small spines and a larger spine projects from the side of the postero- 

 lateral spine near its base. There is a small median dorsal spine on the posterior edge of 

 the carapace, which exposes the last three thoracic somites, and is narrowed posteriorly 



1 Archivf. Nahirgesch., Jabrg. xxviii. Taf. xiii. fig. 1. • Sletamorphose tier Squilliden, fig. 22B. 



