414 SECTIONAL TRANSACTIONS.— C. 



elements. The Caradoc Homalonotid-Acaste fauna (in part of southern 

 origin) spreads from East Shropshire across North Wales and to north 

 and east fringes of Lake District ; it later receives Chasmopids (of Baltic 

 origin) probably from the west. A foreign fauna invades mudstones in 

 Scotland and Central Wales about the time of the Caradoc/Ashgillian 

 junction and the Welsh and Lake District limestones take on a Scots-Irish 

 faunal aspect. Later Ashgillian faunas discussed. Llandovery faunas less 

 differentiated geographically than Ordovician, some genera appear or re- 

 appear earlier in north than in south, ancestral Wenlock elements evident. 

 Wenlock faunas most luxuriantly developed in south-east. Ludlow 

 trilobites (in Anglo-Welsh area only) waning in importance. 



Dr. G. L. Elles. — 2. The Graptolites. 



Graptolites (Graptoloidea) essentially planktonic, distribution intimately 

 connected with mode of life ; effected by currents, whether {a) attached to 

 host, ib) as free swimming germs or (c) as free swimming maturer in- 

 dividuals ; time taken in migration negligible compared with rate of deposit 

 of rocks in which they occur. Factors affecting completeness of succession : 

 (a) quietness of waters ; (6) facies ; (c) structural considerations. Complete 

 succession at any one time may be : (i) Condensed (perhaps planktonic) ; 

 (2) Spread out (drifted) ; (i) is richer fauna, (2) gives relative ages more 

 accurately. Remarkable continuity in faunas where succession complete 

 and fundamental world-wide assemblages at corresponding horizons, some 

 difference in detail in different regions possibly due to migration. 



Analysis of successive Graptolite Faunas of the British Lower Palasozoic 

 Geosyncline in relation to those of extra British areas. Possible interpreta- 

 tion of certain features. 



Dr. A. Lamont. — 3. The Brachiopods. 



Shallow water, sessile ; brief drifting life ; wide or deep seas, muddy 

 belts, climate, land, as barriers. 



Coarse-ribbed Or this carausii (Arenig) in sands. Large body-spaced 

 Poramhonites intercedens (Llanvirn) in limestone indicating clear water. 

 P.filosa (? horizon) in limestone indicating clear water. Small Leptelloidece 

 in muds of Tramore limestone ; higher beds reaching a Mesograptus foliaceus- 

 Nemagraptus gracilis horizon. Common source of Scots, Irish, Welsh 

 faunas about this time. American comparisons. 



Dinor this flab ellulum, Nicolella actonice, Orthis calligratnma, coarse-ribbed, 

 large volume, in sandy limestone or sand ; poor horizon-markers. Com- 

 pressed or diminutive individuals in shales. (?) HjS poisoning. Adaptation 

 to poverty of oxygen in water above mud. Sowerbyella, narrow body uses 

 minimum oxygen, extended margin collects from wide area. Individuality 

 of Anglo-Welsh Caradocian fauna, Wattsella, Kjcerina, not accounted for 

 by sea-floor. (?) Land barrier through Saltees. 



Scots-Irish conquest (Ashgillian) of Anglo-Welsh area ; Schizophorella 

 fallax in Dolhir beds Glyn Ceinog ; Fardenia cf. scotica in Cyrn-y-brain 

 beds, Llangollen. Perc6 (Quebec) comparisons. 



Llandovery — cosmopolitan. Distribution of Pentamerus oblongus. 

 Maroon shales, Walsall boring, current-bedded, large Brachyprion, Schucher- 

 tella, Stricklandia lirata forma typica ; the last in length of apertural margin/ 

 body volume ratio exceeds 5. /jVaf a var. a from coastal sands. Considerable 

 oxygen available due to (i) small organic content of muds, (2) little volcanic 



