PACKARD. ] GEOLOGICAL SUCCESSION OF PHYLLOPODA. 309 
species, differing decidedly from Esthcria morsei or Estheria mexicana. 
It rather approaches HE. jonesii from Cuba in the form of the shell and 
style of marking of the valves. It does not resemble closely any of the 
fossil forms figured in Jones’ Monograph of fossil Estherize. The mark- 
ings, however, present some resemblances to H. middendorfii Jones, but 
differs in the want of anastomosing cross-wrinkles between the ridges. 
One valve and portions of others were preserved; but none of them 
show the breaks (umbones), though the form of the remainder of the 
shell indicates that they were situated nearer the middle of the valve 
than usual, 7. e., between the middle and the anterior third of the shell. 
The shell is deep, probably more so than in ZL. jonesit, though the valves 
have evidently been flattened and somewhat distorted by pressure, but 
apparently the head-end was more truncated than in HL. jonesii, as the 
edge of the shell and the parallel lines (or ridges) of growth along the 
head-end are below bent at right angles to the lower edge of the shell. 
The raised lines of growth are very numerous and near together; they 
are of nearly the same distance apart above near the beaks as on the 
lower edge. The very numerous lires of growth are thrown up into 
high sharp ridges, the edges of which are often rough, finely granulated, 
and often the valleys between are rugose on the surface. In one or two 
places a row of papillee for the insertion of spinules may be seen where 
the shell has been well preserved, aud between many of the lines of 
growth there are irregular superficial ridges. Length 10™™; depth 
coe 
The valve is evidently that of an Estheria, much truncated anteriorly, 
and with the lines of growth much thicker, higher, and closer together 
than in any North American species known to us, and may prove, when 
better specimens are found, to be allied to the Tertiary Siberian Z. 
middendor fii. 
The species is named in honor of the discoverer, J. W. Dawson, LL. D., 
who has so persistently and ably investigated the Leda clays of Canada. 
It should be observed that fig. 4 is not a particularly good representa- 
tion of the fossil. 
A point of a good deal of interest in connection with this Quater- 
nary species is that at present no species of Estheria is known to be 
peculiar to the Atlantic province. Lstheria mexicana, however, ranges 
as far east as Ohio, but this is not at all related to H. dawsoni. he 
question arises where did the latter Quaternary species come from. It 
is not an Arctie form, for no species of the genus is known to inhabit 
the circumpolar region. It would seem as if it had been a Quaternary 
survivor through the glacial period of a southern or Tertiary species. 
Geological Succession.—The following table gives a view of the geologi- 
cal succession of the fossil Phyllopoda; it is compiled from the works of 
T. R. Jones and Gerstaecker, with the additions made, (1878~’81,) since 
the publication of those works. 
Quaternary ....--.-..<- Estheria dawsonit Packard .............------- Leda clay, Canada. 
PRO HAY TE aoe ce Estheria middendorfii Tones .......--..------- Siberia. ; 
Eocene Tertiary .-.... BRAMCHUPUB Peas tease Doe ee beret eee beeene Fresh-water limestone, Isle of 
Wight.* 
MMCBOZ0ICT «2 - c-e eee) Estheria forbesti JOnes.--..------+-s0+-+--+02- South America, 
Wittihereaweccoyasans-- | Matherid elipiicd DUNKEL. snes sls + sss e lec ce Germany, 
: Estheria elliptica var. subquadrata.......--..- Sussex, England. 
Odlitert sss esa 2S Estheria concentrica (Bean) .......-...-..----- Yorkshire, England. 
ih Estheria murchisonie Jones ....-------------- Skye, Scotland. 
i a ie Geological Society of London, 1878. Abstract in Annals and Mag. Nat. Hist., 5th ser., 
1, p. 9, . 
