PIIYLLOCARIDA. 291 



The series of Amphipods begins with Gyamus ceti (Linn.), 

 the whale-louse, passes into Gaprella, with its linear body 

 and spider-like legs, to Hyperia, which lives as a mess-mate 

 of the jelly-fish, Gyanea, and culminates in the water-flea 

 {Gammarus ornatus Edwards) and sand-flea ( OrcAes^m agilis 

 Smith), abundant and leaping in all directions from under 

 dried sea-weed at high-water mark. 



Fig. 259 represents Gammarus rohustus Smith, a fresh- 

 water form common in the western territories. 



Vig. 259.— Gammarus robustus Smith. Utah. Enlarged.— After Smith. 



Order 5. Phyllocanda. — This name is proposed for a 

 group of Crustacea, the forerunner of the Decapoda and 

 hitherto regarded as simply a family {Nebaliadce), in which 

 there is an interesting combination of Copepod, Phyllopod, 

 and Decapod characters, with others quite peculiar to them- 

 selves. The type is an instance of a generalized one, and is 

 very ancient, having been ushered in during the earliest Si- 

 lurian period, when there were (for Crustacea) gigantic forms 

 {Ditliyrocaris was over one foot in length) compared with 

 those living at the present day. The order connects the 

 Decapods with the Phyllopods and lower orders. The mod- 

 ern Nebalia is small, about a centimetre (.40-. 50 inch) in 

 length, with the body compressed, four of the abdominal 

 segments projecting beyond the carapace, the last abdominal 

 segment bearing two large spines. There is a large rostrum 

 overhanging the head ; stalked eyes, and two pairs of anten- 

 nae, the second pair nearly as long as the body and many- 

 jointed. The mandibles are succeeded by two pairs of max- 



