ANNIVERSARY ADDRESS 01? THE PRESIDENT. 



93 



Crustacea. — Only 2 new genera appear with the coming-in of 

 the Lower Tremadoc (Psilocephalus and Neseuretus) ; hut the whole 

 Crustacean fauna comprises 13 genera and 24 species, of which 10 

 genera and 19 species especially characterize the Lower Tremadoc. 

 They are so essential to a right understanding of the Lower Tremadoc 

 rocks and their entire distinctness from the Upper Lingula-flags that 



1 enumerate them : — Agnostus Barloivii, Belt ; A. dux, Call. ; Cono- 

 plirys salopiensis, Call. ; Asaphus Croftii, Call. ; Dionide aira, Salt. ; 

 Licliapyge cuspidata, Call. ; Neseuretus (5 species, all by Dr. Hicks) ; 

 Niobe Homfrayi, Salt. ; N. menapiensis, Hicks ; N. solvensis, Hicks ; 

 Conocoryphe verisimilis, Salt. ; Olenus triarthrus, Call. ; 0. Salteri, 

 Call. ; Psilocephalus injlatus, Hicks ; and P. innotatus, Salt. None of 

 the above species occurs below or above the Lower Tremadoc horizon. 

 The remaining five occur also in the Upper Lingula-flags, and unite the 

 two formations. The chief species named occur at Penmorfa, Borth- 

 wood, and Llanerch in Caernarvonshire, and Dudreath and Tyn-y- 

 llan in Merioneth ; and the same species occur in the St.-David's 

 promontory at Whitesand Bay, &c. Nowhere do the species above 

 mentioned transgress the lower beds ; the Lower and Upper Tre- 

 madoc are connected only by Agnostus princess, Ampyx prcenun- 

 tius, and Ogygia scutatrix. Nothing that I could adduce would be 

 stronger evidence of the value of the Lower Tremadoc as a well- 

 defined zoological group : it contains more genera than any other 

 division of the Lower Cambrian stages ; and the species are essen- 

 tially characteristic. 



Bryozoa. — Bictyonema sociale, Salt., as in the Upper Lingula- 

 flags. This genus occurs near Tremadoc in the passage-beds. 



Brachiopoda. — The Lower Tremadoc Brachiopoda are Kutorgina 

 cingulata, Lingula petalon, Lingulella Nicliolsoni, L. lepis, Obolella 

 Beltii, 0. sabrince, 0. plicata, and 0. sagittalis. Orthis carausii, 

 0. lenticularis, and 0. menapice. 4 of these 5 genera and 6 of the 

 11 species pass to the Upper Tremadoc. They are Lingula petcdon, 

 Lingidella lepis, Obolella Beltii, 0. plicata, Orthis carausii, and 

 0. lenticidaris. 4 genera and 5 species appear from the Upper Lin- 

 gula flags, so that the true Lower Tremadoc species are few, and only 



2 species are peculiar, viz. Lingulella Nicliolsoni and Obolella sabrince. 

 Lamellibranchiata. — The first appearance of this class, or the 



earliest known in the British rocks. Dr. Hicks, through his 

 researches upon the Tremadoc rocks of Eamsey Island, has obtained 

 these first evidences of Pelecypod or bivalve molluscan life. He 

 refers them (and, I think, rightly) to 5 genera and 12 species — 

 Bavidia (2), Glyptarca (2), Modiolopsis (4), Palcearca (2), and 

 Ctenodonta (2) ; none of the species is known out of or above 

 the Lower Tremadoc. 



Gasteropoda. — None known below the Arenig rocks. 



Pteropoda. — The genus TJieca is represented by 5 species in the 

 Lower Tremadoc, viz. TJieca ovata, Salt., T. bijugosa, Salt., T. cuspi- 

 data, T. Bavisii, and T. (Cleidotheca) opercidata. The 3 first 

 named pass to the Upper Tremadoc. T. Bavisii is the only species 

 in the Tremadoc rocks of St. David's. The remaining 4 are North- 

 Welsh Tremadoc species. 



