PIIYLLOCARIDA. 291 



The series of Amphipods begins with Cyamus ceti(L\rm.}, 

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

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

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

 (Gammarus ornatus Edwards) and sand-flea (Orchestia agilis 

 Smith), abundant and leaping in all directions from under 

 dried sea-weed at high-water mark. 



Fig. 259 represents Gammarus rolustus Smith, a fresh- 

 water form common in the western territories. 



Fig. 259. Gammarus robustus Smith. Utah. Enlarged. After Smith. 



Order 5. Pliyllocanda. 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 cpiiite 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 mas- 



