98 
THE VOYAGE OF H.M.S. CHALLENGER. 
I have shown that the Alima larva resembles the adults of the genus Squilla in the 
depression of the hind body, the presence of marginal spines on the dactylus of the rap- 
torial claw, in the small number of marginal spines on the outer edge of the exopodite of 
the uropod, in having its inner spine longer than the outer, with a lobe or dentation on 
its outer edge, and in the presence of numerous secondary spines between the submedian 
spine and the intermediate marginal spine of the telson. 
In all of these respects Alimerichthus resembles Alima ; and it is, therefore, beyond 
question, a Squilla larva, but it differs from Alima in the great width of its telson and 
the absence of spines on its abdominal somites, as well as in its resemblance to the more 
primitive Erichthus larva. 
The comparative study of the adult Stomatopoda teaches that the genera Lysio- 
squilla and Squilla are two divergent branches from a common stem, and that the 
primitive Squillse were more like this stem-form, and therefore more like Lysio- 
squilla than the more specialized species. In the genus Squilla, Squilla ( Chlorida ) 
microphthalma and its allies are the closest living representatives of the stem-form, 
and they resemble the lowest species of the genus Lysiosquilla in the small size and the 
approximation of the eyes, the small size of the antennae and uropods, the loose 
articulation of the hind body, and the width of the telson. I shall show further on 
that the larva of Lysiosquilla, as well as of the more primitive genera of Stomatopoda, 
is an Erichthus, and that all the true Alimas are Squilla larvae. The common ancestor 
of Lysiosquilla and Squilla must therefore have passed through an Erichthus stage. If 
it be true that the characteristics of the Alima larva are the result of secondary 
modification, it is of course quite possible that the most modified adult Squillse 
might have their larvae the least modified, but in the absence of any proof that this is 
the case, it is more natural to believe that the most typical Alimas are the young of the 
most typical Squillas, and that Alimerichthus, the most primitive and Erichthus-hke of 
the Alimae, is the young of a smooth loosely articulated and primitive Squilla, like 
Squilla ( Chlorida ) micro'phthalma. While this conclusion cannot be accepted without 
question, in the absence of direct proof, there is much reason for believing that 
Alimerichthus is the larva of a Squilla closely related to Squilla microphthalma, and 
this decision receives added force from the fact that several of the most conspicuous 
peculiarities of Alimerichthus as distinguished from Alima, such as the width and 
shortness of the telson, and the loose articulation of the hind body, are points of 
resemblance to Squilla microphthalma. In the true Alimae the postero-lateral angles 
of the abdominal somites end in acute spines, which are not developed in Alimerichthus, 
and, as Squilla microphthalma is the least costate of the true Squillas, this is another 
point of resemblance. It is not probable, however, that Alimerichthus is specifically 
identical with Squilla microphthalma, and future research may prove that its adult 
form is an unknown and still more primitive Squilla. 
