StJESS — DISTBinUTION OF TllR BBACIIIOrODA. 
289 
c, One species perhaps first appearing in Utica slate : Le2)t. sericoa. 
d, New speoies, neither found in Trenton limestone nor in Utica 
slate : Discma cultata, D. crassa, D. siibtruncata, Orthis centrilineata, 
0. crisjyata, 0. erratica. 
You easily perceive that the members of group A and a number 
of OrtJddes show other facts of recurrency than the deep sea group 
B, and that they therefore seem to have lived in other conditions, 
viz., probably in another depth. I might even venture to say more 
than that. A certain number of shallow- water Brachiopoda of the 
Trenton limestone reappear in the Utica state ; so also do a number 
of Brachiopoda belonging to a somewhat deeper zone. These latter 
all pass on into the Hudson river gToup, but the shallow-water species 
do not, and are, on the contrary, represented by a number of new 
shallow-water species. In this case, indeed, I presimae tJictt a change 
■in the littoral or sub-littoral zones has taJcen place alone, the fauna of 
the deeper zones remaining the same. 
Above the Hudson river gi'oup the beds of sandstone with lAngula, 
cuneata and ripple-marks follow. 
II. England. 
The association of Orthides with species of the shallow-water 
group A is very nice in the deeper Silui'ian beds. I need only cite 
Sir Roderick Murchison's and Mr. Salter's statements in Siluria, 3rd 
edition, pp. 47, 50, and 53, to show that the oldest fossiliferous depo- 
sits are very nicely characterized by the association of the genera 
Lingula and Orthis. In the calcareous Llandeilo beds of Pembroke- 
shire (Sil. 56), Lept. sericea is cited with Ling, attenuata, L. granidata, 
and Orth. striatula. I believe it might be of some peculiar interejt 
to study the fossils of those localities, where the calcareous portion 
of these beds passes into slates. It must be interesting to see the 
members of deeper zones appearing in this limestone. In comparing 
the lists of Caradoc and Bala Brachiopoda with those of Llandeilo, 
as given in Silm'ia, 3rd edition, and regarding Spirif. insularis as an 
Orthis (SU., p. 209), you may arrive at the following conclusions: — 
Eighteen species of Brachiopoda are known in the Llandeilo beds, 
but all the characteristic genera of the deep sea gi'oup B are wanting. 
The species are divided thus : Five Lingula, one Sophonotreta, ten 
Orthides, two Lept^nse. Of these the following recur in the Caradoc 
and Bala : — 
Of the five Lingula, none. 
Of the one Siphonotreta, none. 
Of the ten Orthides, seven. 
Of the two Leptsense, both. 
The characteristic inhabitants of shallow water, aU remain con- 
fined to the Llandeilo beds, as well as one-thii-d of the Orthides ; on 
vol.. III. 2 0 
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