464 Mr. C. Spence Bate on the British Diastylidee. 



of being recognized by the two pairs of short styliform processes 

 attached to the two anterior segments of the abdomen, analogous 

 to those of the higher types of Crustacea. 



Having traced the forms of the Diastylidce and compared 

 the same with that of the larva of a Macroura-form Decapod, 

 and having, moreover, shown that the former are in a con- 

 dition to continue their species, I think I am in a position to 

 assume that they are Crustacea of adult forms, and that, con- 

 sequently, they are not the young of any of the Decapoda, and 

 that they form several genera in a family essentially character- 

 istic. It now becomes necessary to see where, among Crustacea, 

 this family should be placed, and the comparison of the dissected 

 animal with that of others may lead to an approximation of the 

 truth. 



The carapace is developed upon the type of the Podophthalma, 

 whereas the eyes are sessile ; but in some of the Macroura, as 

 in Athanas and Alpheus^ the peduncles are rudimentaiy : there- 

 fore it is but legitimate to assume that the organs are formed 

 upon the same type, but rudimentary in character, in the Dia- 

 stylidcSj — reduced to this form by the subterranean (?) habits of 

 the animal and the eccentric development of the carapace from 

 the normal form. 



The antennae are generally more or less abortive, and all are 

 typically below the Macroura ; although in some species, as in 

 DiastyliSy there may be observed in the lower antenna an organ 

 which can only homologize with the olfactory organ of the 

 Decapoda (fig. 5 a). 



The mandibles are developed upon the type of those of the 

 Amphipoda rather than upon those of the Macroura or the 

 Stomapoda, although they assimilate to the latter somewhat in 

 the development of the internal lever-like process for the attach- 

 ment of muscles. The maxillae and posterior members all ap- 

 proximate the Stomapod type, as exemplified in the Mysidce, 

 whereas the abdominal segments, except in Bodotria and the 

 closely allied genus Venilia, are mostly wanting. 



Taking these several distinctions into consideration, there can, 

 I think, be little doubt,— 



1st. That the animals are adult Crustacea. 



2nd. That they belong to the suborder Stomapoda. 



3rd. In that suborder they rank after the Mysidce, that is, 

 they hold the lowest position known among the Stomapoda ; but 

 that they indubitably belong to that suborder, — not to the sub- 

 order Decapoda Macroura, as suggested by Goodsir, and repeated 

 with doubt in the ' British Crustacea.' 



