ANNIVERSARY ADDRESS OF THE PRESIDENT. 



sagittalis, and Dictyonema sociale. 42 species are known in North 

 Wales, and 30 in South Wales ; yet, as before stated, only 3 species 

 are common to both districts — Niobe Homfrayi, Lingulella Davisii, 

 and L. lepis. 



It must be observed that no species of true Graptolite is known, 

 in the Tremadoc rocks, none being really known below the Arenig 

 in Britain, Europe, or America. Doubtless the whole Arenig series 

 is more closely allied to the succeeding and overlying Llandeilo than 

 to the underlying Tremadoc ; it is certainly so as exhibited in the 

 South-Wales promontory, where both groups are typically developed 

 and succeed each other in one continuous and conformable section ; 

 yet there is perhaps no greater change or pakeontological break be- 

 tween any two conformable British groups than between the 

 Tremadoc and Arenig, the rich Hydrozoal fauna coming in at the 

 close of the former and commencement of the latter. The change 

 in the physical conditions of the sea and sea- bed at the close of the 

 Tremadoc period was favourable to the development of this division 

 of the Ccelenterata. 



The most characteristic of all the fossils of the Lower Tremadoc 

 are Niobe Homfrayi, N. menapiensis, Psilocephalus innotatus, with 

 Angelina SedgwicJcii and Asaphus affmis in the Upper Tremadoc ; 

 these five species are met with wherever the Tremadoc rocks are 

 well seen. Agnostus princess, so abundant in the Upper Lingula- 

 flags of North AVales, is not known in the St.-David's Tremadoc 

 sections, and is of the rarest occurrence in the North- Welsh classical 

 localities ; with Agnostus the characteristic Lingulella (L. Davisii) 

 dwindles away, and seems to be replaced by the small but equally 

 gregarious L. lepis. 



The true Upper Tremadoc series is characterized by many new 

 species. Niobe Homfrayi, Psilocephalus innotatus, and P. inflatus 

 no longer exist as species, but are replaced by Asaphus Homfrayi 

 and Angelina SedgiuicJci : Cheirurus Frederici at Garth, Llanerch, 

 Penclogwyn, Portmadoc, &c, ranges from the top of the Lower, 

 through the passage-beds, and all through the Upper Tremadoc into 

 the Arenig. Olenus impar adds another to the characteristic species 

 of the Upper Tremadoc ; and Oyrtoceras prcecooo, which occurs at 

 Llanerch, is the earliest known Oephalopod in the British rocks. 

 The first Orthoceras (0. sericeum) known* also occurs in the passage- 

 beds at Garth and Tuhwnt-yr-bwlch. 



It is clear that there is no stratigraphical or palseontological 

 break between the Lingula-flags and the Tremadoc : both areas 

 prove the former by direct evidence ; and 9 species connect them 

 palseontologically, viz. Dictyonema sociale, Salt., Agnostus princeps, 

 Salt.. Ampyx prcenuntius, Salt., Conocoryphe depressa, Salt., ? Olenus 

 impar, Salt., Lingulellu Davisii, M'Coy, Z/. lepis, Salt., Obolella sagit- 

 talis 1 ?, Salt., Orthis lenticularis, Wahl. Three of these same species 

 also connect the Tremadoc and Arenig : they are Lingulella Da- 

 visii, L. lepis, and Orthis lenticularis. All palseontological evidence 

 goes to prove " that the Tremadoc rocks of the St.-David's area are 

 closely allied to, if not identical with, the lower portion of the 

 * Originally in the cabinet of Mr. D. Homfray, of Portmadoc, 



