446 GEOLOGICAL SURVEY OF THE TERRITORIES. 
(in Peltocaris minute) spines. In the presence of the telson in the typi- 
cal fossil genus Ceratiocaris we certainly have an important character 
separating the type with its allies from Nebalia, and allying them to 
the Decapods; and thus in the provisional synopsis of the order pre- 
sented farther on, we have placed the fossil forms in a separate suborder 
from the Nebaliade. 
CLASSIFICATION OF THE SUBCLASSES AND ORDERS OF CRUSTACEA. 
3 E Ss = 
S S 3 3 
Ss S S . ORD) 
gz Ss yy 3S ‘ ayy 
3 = Ss S 3 2 
S S = es 
S os is) Re cS ° = 
s = S = S 8 
Dm Ss S = = S op 
DS SS LS » En 3 ~ g 
Eat Ree i PMY SINS = Sig 
= ~~ 
| a) es = E 
= a 
Ry = By iS 
eae y i 
nd) \ Samm aie oe 
NEOCARIDA. PAL AOCARIDA. 
CRUSTACEA. 
While the posterior edges of the abdominal segments in Hymenocaris 
appear to be spined as in Nebalia, there are some characteristics of im- 
portance in the fossil forms which deserve mention; these are the sculpt- 
ured carapace, especially of Dictyocaris, in which the surface is reticu- 
lated.! Moreover the size of these genera was enormous, but if we, as 
we seem to be warranted in doing, regard Nebalia as a survivor and 
decrepit or old-age type of the order, which has lost the ornamentation 
of the integument, the size, and the telson even, being dwarfed, smooth- 
skinned, and in general very simple compared with the forms which 
existed at the time when the type culminated and before it began to 
die out, we may have an explanation of the greater simplicity of the 
carapace and abdomen of Nebalia, as compared with its paleozoic an- 
cestors. 
From our total lack of any knowledge of the nature of the limbs of 
1It should here be remarked that while the carapace of Nebalia is smooth, upon 
making a section of it areticulated structure is plainly seen in the parenchyma or soft 
parts of the shell, but it is entirely too minute to be perceptible in the shell even under 
high powers. This structure may be comparable with that of Dictyocaris, especially 
as Salter remarks (Ann. and Mag. Nat. Hist., 1866, p. 161): ‘‘ The entire surface of the 
carapace is marked with hexagonal reticulations one-thirtieth of a line in diameter, 
of which the aree are convex and the bounding lines sunk on the exterior aspect. 
This would, I think, indicate the ornament to be connected with the structure of the 
carapace rather than to be a mere external sculpturing. As no films can be obtained 
thick enough to furnish a section for microscopic examination, the point cannot be 
ascertained,” 
