New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1879-09-06

FL Resignation Of Go'T salsr from tho
classes displayed in the Lower Siurian were la ox-
isteuce 1T the close of the Upper Siluriau.
H.-DIsPLAY OF GROUPS or TRIBES BY PERIODS.
The Crustaceans of the Primordai period repre-
sent three distinct gronps-the Fulohites. Ply lo-
pods and Ostracoids. All Of these continued 10
the close of the Silurau. and beyond. receiving Ia
the Lower Heidelberg period an addition 10 their
ranks IN the shape OF the Eurypterils. Fig. 3 of
article . represents a Primordial PAyllopcd. and
Gr Of article an Upper SilurIan O3trac0d. The
shell-inhabitng tribe Of Worms, or Tubicola, the
tribe to which the Primordal SaPuh'e' belongs,
extends through tho whole Silhran, does also the
naked group OF Anneids, as proved by their tracks
and borings. The Orthis group among BrachOpods,
which began ia the Prmordia runs through the
entire system increasing in force 10 the close
Of the later Slurian species attaining eNtraord
nary size Sec article g. The Radate tribe of
Cvstlds, which began in the Primorial, attained,
as have shown in article !, its greatest expan-
sion IN the Trenton period, aud disappeared alto
gether during the Oriskany. The Grind or Lily
encrinIte tribe which began n little later. or in he
Canadian Rod, attans, on the contrary, ITS maxi
mum display in post-Siluran time, though wonder
fully brought ont in the Trenton, Niagara and
Lower Heidelberg periods Another tribe, the
Graptoiites. which likewise began in the Primor-
period. and ceased 10 exist as true Graptolites dur
ing the Niagara. The remarkable group OF cup
sponges. of which the Archgocyd'hHs is the type
lsee articles and 81 passes from the Pnmordial
into the Canadian. but is unknown In the forma-
tons of later periods. We thus see that while new
tribes were coming in, old ones we're dying out,
and so il has been throughout geological time.
uI-DisPLAY OF GENERA AND SPECIES BY PERIODS.
To treat this subject with any degree of fulness
would require n great deal of space. and shall
therefore notice only the more important facts.
The dominant forms OF the Prmorial period Were
the Trlobites these leading in genera and species
all Others but the majority Of the genera and all of
the species end with the period In the Canadian
Ierod there appear. along with some OF the Old
genera, a number of new ones and an entirely
different range Of species. In the Trenton period
the number of Primordial genera is still further
reduced IA single one having been recognizsdl.
other genera are introduced apparently to fill up
the gaps made by the disappearance of the Primor
dial types, and the species again almost wholly
changed The same thing was repeated in the
earlier Upper surlan. after which time the tribe
began to decline. Bat as have previously stated
lartice o. il was ia full force when the first Of the
Emyptai IDS came upon the scene.
The OstracOids eliminated in the later Upper
Silurian, number of new genera being here added
to Leperdisa and Beyrchia. which began III the early
Lower Siluran aud extend, under various specific
forms. through the whole systems while to the
Primordial Hymeaocdyis tsee art. p among Phyilo-
pods there succeeded few other genera, both in
the Lower and Upper silurian. one of the most re-
markabe forms being the Ceratiocdris. an Upper
Silurian type
Few additions made in the course Of the
Upper Silunan to the genera Of Cephalopods that
began In the Lower silurian, but the species OF
different periods different The same Is true OF
the Gasteropods aud Acophalaj but the Brachio-
pods were almost constantly receiving now