88 Journal Xew York Entomological Society. [^'°'- -^>^i-^. 



logons with the mandihles of Crustacea are more limb-like, or are not 

 of the true "jaw" type. 



The fact that the incisor process "in" of A'cbolia (Fig. lo) is 

 but weakly developed, and the differentiation of the masticatory 

 region is consequently not so marked as in the higher forms, would 

 indicate that Nebalia is a comparatively primitive type but little higher 

 than the Branchiopoda, Copepoda, etc. ; while the fact that Nebalia 

 exhibits a marked tendency toward a differentiation of the mastica- 

 tory area and the development of an incisor process (even though a 

 feeble one), shows that Nebalia is structurally intermediate between 

 the lower Crustacea and the more modified forms, as is borne out by 

 the character of the body in general. The great size of the mandib- 

 ular palpus (in comparison with the size of the basal segment of the 

 limb which forms the mandible proper) and its apparent ability to 

 function in locomotion, is another feature indicating the compara- 

 tively primitive character of Nebalia, and the evidence of the man- 

 dible is in full accord with other indications of the intermediate 

 position of Nebalia as a form connecting the lower Crustacea 

 (Branchiopoda, Copepoda, Ostracoda, etc.) with the more modified 

 types. Nebalia has not developed a lacinia mobilis (and gnatho- 

 fimbrium), and on this account the absence of a lacinia mobilis in the 

 mandibles of certain Crustacea may possibly be regarded as some- 

 what more primitive condition than is the case with those Crustacea 

 in which the lacinia mobilis is developed. 



The Euphausiacea, such as Tliysaiiopoda, are very primitive types 

 related to the Decapoda. and since both of these oi'ders have not 

 developed a lacinia mobilis (see Fig. 35) in the mandible (and the 

 gnathofimbrium is usually lacking also"), this fact would support the 

 view that the Decapoda and Euphausiacea are quite closely related. 

 The Stomatopoda such as SqitiUa (Fig. 28) are rather primitive forms 

 in some respects, and their mandibles also lack the lacinia mobilis 

 as in the Euphausiacea and Decapoda, which they resemble in cer- 

 tain other anatomical features as well. 



The Mysidacea such as Mysis (Fig. 7) have developed a lacinia 

 mobilis " li>i," and a primitive sort of gnathofibrium " gf," and in this 

 respect they resemble the Cumacea (Fig. 2), Tanaidacea (Fig. 3), 

 Isopoda (Figs, i and ^6) and related forms, as was first pointed out 



