334 SYNOPTIC COLLECTION. 



antennae are largely developed and these were probably 

 used as locomotor organs. The mouth parts are not pre- 

 served, so that their structure is not known. The thoracic 

 legs extend forward; they are undivided at their ends, and 

 the anterior pairs are apparently not differentiated into 

 organs of prehension or mastication, but all are useful as 

 swimming organs. Most of the abdominal segments bear 

 .a pair of appendages which are simple in structure (fig. 

 2, enlarged four times), and like the thoracic appendages 

 were used in locomotion. The last segment or telson 

 carries a pair of swimmerets (fig. 3) which indicate that 

 this portion of the abdomen is a true segment, and which 

 also give additional proof that Palaeocaris was a good 

 swimmer. 



It is generally conceded that the Malacostraca can be 

 traced back to the group described by Packard as the 

 Phyllocaridae, the only living representative of which is 

 Nebalia. One of the ancestors of Nebalia is probably 

 Ceratiocaris (PI. 823, C. papilio Salter), in which a cara- 

 pace covers the thorax and a part of the abdomen. The 

 antennae are obscure and are indicated in the figure by 

 broken lines. The anterior projection of the carapace or 

 the rostrum ( PI. 823) has separated from the carapace. 

 The resemblance of Ceratiocaris to Nebalia is marked. 

 The latter is a generalized form combining Copepod, Phyl- 

 lopod, and Decapod features. 1 The development is with- 

 out a metamorphosis and the young and adult resemble 

 each other. Nebalia bipes Fabr. (No. 824; PL 825, figs. 

 1-6, Nebalia geoffroyi) is a marine form which has the 

 segments of the thorax and abdomen similar and distinct, 

 though all of the former and four of the latter are covered 

 by a carapace (fig. i, nearly natural size). In fig. 2 one 

 side of the carapace has been cut away exposing the body 

 beneath. The eight thoracic segments can be easily 

 counted, and each carries a pair of appendages in the 



1 Woodward, Quart. Journ. Geol. Soc. London, LI, 1895, p. 

 Ixxxiii. 



