PACKARD.] GENEALOGY OF CRUSTACEA. AIT 
their paleontological history, the latter being an important check upon 
any errors arising in the former. 
It has seemed to us the more natural view that the systematic posi- 
tion and relations of the 
Phyllopods, as compared “i 
with the Cladocera, is that : 
the Phyllopods are simply 
a highly developed and ex- 
tremely specialized branch 
of a Cladocerous stem ; that 
the Cladocera are a step 
higher than the Ostracoda, 
which connect the Bran- {i 
chiopoda with the Copepoda. |\\\\ 
There is a tolerably com. /\\\\\ 
plete ascending series of | 
forms, beginning with the 
. ° Fic. 47.—Nauplius of Branchi- Fig. 46.— Advanced 
Copepoda and culminating pus stagnalis. After Claus. larva of Lepidurus en- 
in the Phyllopods. Here larged. After Brauer. 
we should stop, and in endeavoring to account for the origin of the De- 
capoda, we do not see what facts there are to sustain the view that the 
highly specialized Decapoda, much less the Tetradecapoda, originated 
from the Phyllopods or forms like them. The more natural view 1s that 
the Malacostraca originated by a direct line of ancestral forms, resem- 
bling the zoéa, protozoéa, &c., beginning with a Nauplius condition; 
the development of Penewus and Leucifer giving us data for such a by- 
pothesis. 
Hence the Phyllopods and Decapods, for example, for a time proba- 
bly followed the same developmental path or rather parallel paths. The 
Phyllopods, culminating in the highly specialized peculiar type of Apo- 
dide and especially the Branchipodide, were the flowering out or con- 
sumation of, so to speak, the Branchipodous branch of the Neocaridan 
crustacean tree. On the other hand the Decapods, beginning with the 
Nauplius form, perhaps more rapidly and by an accelerated course of 
development comparatively late in paleontological history, assumed the 
primitive Decapodous characteristics perhaps before the Phyllopodous 
type had been perfected, but in the Tertiary Period culminated in a great 
profusion and luxuriance of forms, remarkable for the number of species 
and variety of shapes of macrourous and especially brachyurous types. 
The paleontological history of the Neocarida, as we have endeavored 
to show by the diagram on p. 361, shows that the shrimps existed dur- 
ing the Devonian,! that the crabs were already in existence during 
the Carboniferous Period, before the Apodidw and Branchipodide had, 
judging by their fossil remains, appeared; while the Limnadiada, gen- 
uine Phyllopods, appeared before any Decapods in the Devonian, the 
Ostracodes being abundant in the Lower Silurian strata. It seems tous 
therefore most probable from a geological standpoint that the Decapods 
could not have originated from the Phyllopods, as the two types were 
developed during the Palzeozoic era. 
That the Phyllocarida were developed independently either of the 
- Phyllopods or of the Decapods seems probable from the fact that the 
Phyllocaridan type became established as early as the Lower Silurian. 
We shall see that the Phyllocarida are not related to the zoéa of Dec- 
apods, and that the Decapods probably did not originate from them. 
' Palwopalemon newberryii has been described by Whitfield from the Devonian of 
Ohio. 
27 
