PACKARD.] 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 Nebalia, 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, ete., 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 zoéa or larva of the Decapods, but no zoéa has a telson, though 
one is developed in a postzoéal 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. ‘Che natural conclusion, in the light of our present knowl- 
edge, is that they are members of the group represented by the existing 
Nebalia. ; 
In order, then, to summarize our present knowledge of the living Ne- 
balia 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. 
External diagnostic characters of the order.—Body compressed; con- 
sisting of 21 segments, 5 cephalic, 8 thoracic, and 8abdominal. Carapace 
compressed, with no regular hinge, 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 antenne, 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 maxill#; 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 appendages (cercopoda). No telson present in 
the living species; well developed in the Ceratiocarida. Young deyvyel- 
oped in a brood sac; development direct; no marked metamorphosis ; 
the young but slightly differing from the adult. 
Remarks.—By the sum of the foregoing characters the Phyllocaridz 
appear to be excluded from any other group of Neocaridan Crustacea. 
1Close scrutiny of specimens in existence may yet show 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 
papilio, but the figure appears to us rather to represent a 4-jointed piece 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. 
