638 ME. E. J. MIERS OTT THE 



Fara. i. Maiid^e. Eyes retractile into orbits. 



Fam. ii. TYCiiiDyE. Eyes retractile beneath carapace ; no orbits. 



Earn, iii. EurypodidjE. Eyes retractile to sides of carapace. 



Earn. iv. Leptopodid^. Eyes not retractile. Legs very long. 



Earn. V. Pericerid.'E. Byes not retractile. Legs of moderate length. 



Witli respect to this arrangement I may observe, in the first 

 place, that the retractility or non-retractility of the eyes is scarcely 

 a character that can be nsed for separating the families ; for in 

 many of the Leptopodiiclse the eyes are capable of a certain 

 degree of mobility, and in many Periceridse they are, as Stimpson 

 has pointed out, completely retractile within the orbital cavity. 

 It is somewhat remarkable that Dana did not observe the cha- 

 racters that are afforded by the structure of the orbital region 

 itself, taken in conjunction with the concurrent modification of 

 the form of the basal autennal joint, to wdiich attention had already 

 been drawn by Milne-Edwards, and Avhich, I am convinced, offer 

 far better distinctions for a natural arrangement of the various 

 groups. Within his first family (Maiidse) Dana includes most of 

 the genera referred by me to the Maiidce and Pericerid£B ; his 

 second family (Tydhidse) contains but three genera, whereof the 

 last, Oamposcia, has but little affinity with the two preceding ; 

 the third (Emypodidae) also includes but three genera, all refer- 

 able to my family Inachidfe ; the fourth (Leptopodidse) cor- 

 responds, with the exception of Inaclioides, to my subfamily 

 Leptopodiinae. The fifth (Periceridse) is a somewhat heterogeneous 

 group ; but the majority of the genera included in it belong to my 

 subfamily Acanthonychinse of the family Inachidse. 



The subfamilies of the Maiiuea instituted by Dana appear to 

 me to be unnecessarily numerous, and are for the most part 

 founded upon characters of minor importance, i. e. the form of 

 the carapace and rostrum. His minor subdivisions, indeed, are 

 less natural than those of Milne-Edwards ; but to him belongs tho 

 merit of having recognized that the Parthenopiuea form a group 

 equal in value to the remainder of the Oxyrhyncha (with tho 

 single exception of Oncinopus). 



M. Alphonse Milne-Ed wards, by whose finely illustrated memoirs 



• our knowledge of the genera of Oxyrhyncha has been so greatly 



increased, lias not, I believe, published any classification of tho 



group ; but in his classification of the Braehyura set forth in the 



introductory portion of his ' Histoire naturelle des Crustaee.^ 



