PACKARD.] FOSSIL ALLIES OF NEBALIA. 443 
as procephalie lobes with eyes, all these parts not being developed in 
the embryo Myside. ; 
But whatever may be said of the resemblances between Nebalia and 
the Myside at an early period after the nauplius stage has been dis- 
carded, when we compare the later stage represented by Metschnikotf’s 
fig. 19 (our fig. 68, in text) with the latest larval stage of Pseudomma 
(see Sars’s figure, our Plate XX XVIII, fig. 5), then we see that the 
diagnostic ordinal characters of the Phyllocarida have declared them- 
selves. There are to be seen in Nebalia the large movable rostrum, the 
compressed pseudobivalvular carapace, the lack of maxillipedes, the 
eight pseudophyllopod thoracic feet, four pairs of abdominal feet, out 
of the six of the adult. On the other hand, in Mysis of the same stage, 
the two pairs of maxillipedes are well developed, and the six pairs of 
remarkably long thoracic feet (the first pair modified maxillipedes) are 
present. There is little to indicate that the Schizopods have descended 
from a Nebalia-like form, but rather from some accelerated zoéa form ; 
‘while, as we attempt in this essay to show, the Phyllocarida have had 
no Decapod blood in them, so to speak, but have descended by a sep- 
arate line from Copepod-like ancestors, and culminated and even began 
to disappear before any Malacostraca, at least in any number, appeared. 
IIl.—THE PALEOZOIC ALLIES OF NEBALIA. 
Having studied the anatomy and development of Nebalia we are pre- 
pared to compare it with a group of fossil forms which are scattered 
through the older Paleozoic rocks from the lowest Silurian to the Car- 
boniferous. In a brief article! Mr. Salter, nearly twenty years since, 
sketched out the characters and showed the relationship of Ceratiocaris 
and a number of allied forms to Nebalia in the following paragraph : 
‘Before the structure of Ceratiocaris was known, of which genus a 
reduced figure is here given, the rostral portion of Peltocaris could not 
have been understood. But a reference to the accompanying series of 
wood-cuts will show that a tolerably broad rostrum, placed in the same 
relative position, occurs in Ceratiocaris. Inthe recent Nebalia itis fixed, 
and in Dithyrocaris and other genera it is perhaps yet to be discovered. 
Again, Ceratiocaris, together with its movable rostrum, has a bivalved 
shell, yet habitually keeps its valves half closed, as I learn from per- 
fect specimens.” 
Salter then enumerates the characteristics of the fossil genera, begin- 
ning with Hymenocaris, which he considers the more generalized type, 
and in the wood-cuts which we partly here produce shows the geologi. 
cal succession of these genera, which also serves as a genealogical table- 
He regards them as Phyllopods, associating Estheria and Apus, regard- 
ing the latter as “the most complete and decided form, and it is one of 
the latest of the group, as it commences in the Trias.” He also says: 
“The links between these coal-measure forms and those of recent times 
are many of them wanting; but in Nebalia we have a good representa- 
tive of the compact, shield-shaped form of Ceratiocaris, the two valves 
soldered into one, and the rostrum attached, the eyes being still beneath 
the carapace.” It is evident from this that Mr. Salter regarded the fos- 
sil genera he enumerates as allied to and as the ancestors of Nebalia, 
and as representatives of it in Paleozoic times. He evidently adopted 
the views of Milne-Edwards and others as to the Phyllopodous nature 
of Nebalia. 
1On Peltocaris, a new genus of Silurian Crustacea, by J. W. Salter, Quarterly Jour- 
nal of the Geological Society of London, vol. xix, 1863, p. 87. 
