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. 



lu all of these respects Alimerichthus resembles Alima, and it is, therefore, beyond 

 question, a Squilla larva, but it differs from Alima in the great widtli 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 Squillie were more like this stem-form, and therefore more like Lysio- 

 squilla than the more specialized species. In the genus Squilla, Squilla (CJilorida) 

 microphthalma and its allies are the closest living representatives of the stem-form, 

 and they resemble the lowest species of the genus Lysiosqmlla 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 Alima} 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 Alim^ are the young of the 

 most typical Squilla^, and that Alimerichthus, the most primitive and Erichthtts-hke of 

 the Alimai, is the young of a smooth loosely articulated and primitive Squilla, like 

 Squilla {Chlorida) microphthalma. 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 microp)hthalma. In the true Alim^e 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 Squilla^, 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. 



