PACKAED.] THE ORDER PHYLLOCARIDA. 447 



the fossil Phyllocarida, we have to be guided solely by analogy, often 

 an uncertain and delusive guide. But, in the absence of any evidence 

 to the contrary,^ there is every reason to suppose that the appendages 

 of the head, thorax, and abdomen were on the type of ISebalia, since 

 there is such a close correspondence in the form of the carapace, rostrum, 

 and abdomen. 



But whatever may be the differences between the fossil forms repre- 

 sented by Ceratiocaris, etc., they certainly seem to approach Nebalia 

 much nearer than any other known type of Crustacea ; they do not be- 

 long to the Decapods ; they present a vague and general resemblance 

 to the zoea or larva of the Decapods, but no zoea has a telson, though 

 one is developed in a postzoeal stage ; they do not belong to any other 

 Malacostracous type, nor do they belong to any existing Entomostracous 

 type, using those terms in the old sense. No naturalist or paleontolo- 

 gist has referred them with certainty to the Decapods, or to any Crus- 

 tacean type than the Phyllopods. To this type (in the opinion of Metsch- 

 nikoff and Claus, who have studied them most closely) they certainly 

 do not belong ; -and thus, reasoning by exclusion, they either belong 

 to the group of which Nebalia is a type, or they are members of a lost, 

 extinct group. The natural conclusion, in the light of our present knowl- 

 edge, is that they are members of the group represented hj the existing 

 Nebalia. 



In order, then, to summarize our present knowledge of the living JVe- 

 halia and its fossil allies, we will give what we regard as the characters 

 of the group and subdivisions, which may be regarded as provisional, 

 though perhaps of some present use. 



Order PHYLLOCARIDA Packard. 



Bccternal diagnostic characters of the order. — Body compressed; con- 

 sisting of 21 segments, 5 cephalic, 8 thoracic, and 8 abdominal. Carapace 

 compressed, with no regular hing^, loosely attached to the body by an 

 adductor muscle ; with a movable rostrum inserted in a depression in 

 the front edge, the carapace covering the basal joints of the abdomen. 

 One pair of stalked eyes ; no simple eyes. Two pairs of well-developed, 

 many-jointed, long, large antennse, the first pair biramous, the 2d pair 

 with a very long flagellum in the male. Mandibles weak, with a remark- 

 ably long 3-jointed palpus. Two pairs of maxillsej the first with a re- 

 markably long, slender multiarticulate exopodite; 2d pair well devel- 

 oped, biramous; no maxillipedes; 8 pairs of biramous, broad, thin, re- 

 spiratory, thoracic feet, not adapted for walking ; the exopodites divided 

 into a gill and flabellum; 4 pairs of large and 2 pairs of small abdominal 

 swimming feet ; no appendages on the 7th segment, the terminal one 

 bearing two long caudal ajjpendages (cercopoda). No telson present in 

 the living species; well developed in the Geratiocaridw. Young devel- 

 oijed in a brood sac; development direct; no marked metamorphosis; 

 the young but slightlj^ differing from the adult. 



Remarhs. — By the sum of the foregoing characters the Phyllocaridae 

 appear to be excluded from any other group of Neocaridan Crustacea. 



1 Close scrutiny of specimens in existence may yet sliow indications as to the nature 

 of the limbs; for example, Salter figures, in the Annals and Magazine of Natural 

 History, 3d series, vol. 5, 1860, p. 154, fig. 3e, what he calls the jaws of Ceratiocaris 

 2}apiUo, but the figure appears to us rather to represent a 4-jointed jiiece of an anten- 

 na. In fig. 2 there are represented the tergal portion of seven segments lying under 

 the carapace. If fresh attention were directed to the discovery of the nature of the 

 limbs success might result. 



