SUESS — DISTEIBUTION OF THE BRACHIOPODA. 



289 



c, One species perhaps first appearing in Utica slate : Le]pt. sericea. 



d, l^ew speoies, neither found in Trenton limestone nor in Utica 

 slate : Discina cuUata, D. crassa, D. suhtruncata, Orthis centrilineata, 

 0. cris'pata, 0. erratica. 



You easily perceive tliat the members of group A and a number 

 of OrtMdes 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 group, 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 presume that a change 

 in the littoral or sub-littoral zones has taken place alone, the fauna of 

 the deeper zones remaining the same. 



Above the Hudson river group the beds of sandstone with Lingula 

 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 Silurian 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 cited with ZriVi^. attenuata, L. granulata, 

 and Orth. striatula. I believe it might be of some peculiar interest 

 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 Siluria, 3rd edition, and regarding Spirif. insularis as an 

 Orthis (Sil., 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 group B are wanting. 

 The species are divided thus : Five Lingula, one Sophonotreta, ten 

 Orthides, two LeptaenaD. 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 Leptsenae, both. 



The characteristic inhabitants of shallow water, all remain con- 

 fined to the Llandeilo beds, as well as one-third of the Orthides ; on 



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