42 NATURAL HISTORY OF ARTHROPODS. 



SUB-CLASS III. PODOPHTHALMIA. 



This division receives its name from the fact that the eyes are situated upon mov- 

 able peduncles ; and while this feature of itself is of slight importance, arid, moreover, 

 is not found in all members of the group, and, on the other hand, exists among the 

 Tanaidae, which have a doubtful position among the Isopoda, and the Phyllopods, still the 

 character is so nearly universal that we may be permitted to employ the name for the 

 group. The name Decapoda, which we have employed to designate a single order, is 

 frequently used as synonymical with Podophthalmia, but it is even more inappropriate 

 than that term for the whole group. 



The general characters of the order are a body of twenty segments, as in the Edrioph- 

 thalmia, a carapax which extends over some, if not all, of the thoracic somites ; the 

 two pairs of antenna are always present, the eyes (except in Cumacea and one or two 

 aberrant forms) are well developed, and placed on jointed peduncles. Respiration is 

 effected by well-developed gills, and in their development the Podophthalmia usually 

 pass through a more or less complicated metamorphosis, in which, in contradistinction 

 to the lower sub-classes, a nauplius stage is rare. 



Though this sub-class has been the subject of more study than any other group of 

 Crustacea, its classification is as yet in a very unsatisfactory condition. For our present 

 purposes the following grouping, which fairly represents our knowledge of the subject, 

 may answer: Order I., Phyllocarida ; Order IL, Schizopoda; Order III., Decapoda; 

 Order IV., Stomatopoda ; Order V., Cumacea. 



ORDER I. - - PHYLLOCARIDA. 



This group, which is represented on the eastern coast of North America by two 

 species of JVebalia, a northern JV. bipes and an as yet undescribed species from 

 Florida, is of very uncertain position, some classing it with the Phyllopoda, others with 

 the Podophthalmia, while Dr. Packard prefers to con- 

 sider it as distinct from both. With this uncertainty 

 it may be well to allow it for the present to remain 

 near Mysis, to which it is evidently closely allied. 

 Nebalia has a compressed body. The rostrum is 

 articulated to the carapax. The second pair of an- 

 temuB are nearly as long as the body. Three pairs of 

 mouth-parts are present, and following them are eight 

 pairs of short leaf-like feet with respiratory functions. Next come four large and 

 two small pairs of abdominal feet (the latter inadvertently omitted in the cut). The 

 last abdominal segment terminates in two large spines. 



As has been said, the development closely resembles that of Mysis, and the animal 

 hatches with all of its appendages outlined, although there exists a time, while the 

 embryo is within the egg, when the features of the nauplius are hinted at, followed 

 by another which recalls the zoea of the Decapoda. Doubtless Dr. Packard is correct 

 in following S alter and Huxley in regarding the fossil forms which occur in the strata 



