PACKAED.] THE ORDER PHYLLOCARIDA. 445 
we have obtained more precise explanations as to the nature of their 
limbs. 
“It is in the highest degree probable, however, that all these forms 
are not true Phyllopods, but have belonged to a type of Crustacea, of 
which now there are no living representativ es, but which, taking their 
origin from forms allied to the lower types of Entomostraca, have pre- 
pared the way for the Malacostracan type. Such a connecting link, which 
has served to the present day, we evidently find in the genus Nebalia. 4 
In 1879, without knowing the views of Claus, just quoted, we pub- 
lished the following brief notice of the leading’ characteristics of the 
group, and proposed that the paleozoie fossil forms, Ceratiocaris, etc., 
be united with the Nebaliade to form a separate order of Crustacea 
under the name of Phyllocarida. 
“The Nebaliadew, represented by the existing genus Nebalia, have 
generally been considered to form a family of Phyllopod Crustacea. 
Metschnikoff, who studied the embryology of Nebalia, considered it to 
be a ‘Phyllopodiform Decapod.’ Besides the resemblance to the Deca- 
pods, there is also a combination of Copepod and. Phyllopod character- 
istics. The type is an instance of a generalized one, and is of high an- 
tiquity, having been ushered in during the earliest. Silurian Period, 
when there were, when we regard the relative size of most Crustacea, 
and especially of living Nebalia, gigantic forms. Such was Dithyro- 
caris, which must have been over afoot long, the carapace being 7 inches 
long. The modern Nebatia is small, about half an inch in length, with 
the | body compressed, the carapace bivalved as in Limnadia, one of the 
genuine Phyllopods. There is a large rostrum overhanging the head; 
stalked eyes; and, besides two pairs of antenne and mouth parts, eight 
pairs of leaf- Hike, short, respiratory feet, which are succeeded by swim- 
ming feet. There is no metamorphosis, "development being direct. 
‘‘ Of the fossil forms, Hymenocaris was regarded by Salter as ‘the more 
generalized type.’ The genera Peltocaris and Discinocaris characterize 
the Lower Silurian Period, Ceratiocaris the Upper, Dictyocaris the Up- 
per Silurian and the lowest Devonian strata, Dithyrocaris and Argus the 
Carboniferous Period. Our existing northeastern species is Nebalia 
bipes (Fabricius), which occurs from Maine to Greenland. 
‘‘The Nebaliads were the forerunners of the Decapoda, and form, we 
believe, the type of a distinct order of Crustacea, for which the name 
Phyllocarida is proposed.” 
A slightly fuller account of the order was also published in the 
writer’s Zoology,” and the order Phyllocarida was placed (pp. 325, 326) 
below Tetradecapods and Decapods, the scheme then presented being 
on the following page: 
On examining the figures of Salter and of Barrande, for we have been 
unable to study any of the fossils themselves owing to their extreme 
rarity, the relationship to Nebalia is very marked, as seen in the form 
of the carapace, the nearly free or detached rostrum, unless the separa- 
tion took place after the death of the animal, and also of the rather long, 
slender abdomen. Upon examining theappendages at the end of the ab- 
domen there is to be seen an important distinction from Nebalia; along, 
slender telson is usually present, with a single pair of large caudal sty- 
lets, or cercopoda, in form like those of Nebalia. But in Hymenocaris 
and Peltocaris the telson appears to be represented by a pair of small 
1The Nebaliad Crustacea as types of a new order. By A.S. Packard, jr. American 
Naturalist, February, 1879, vol. XIII, p. 128. 
2American Science. Series. Zoology for High Schools and Colleges, 1st edition, 
1879. 12°. H. Holt & Co., New York. 
