SECTIONAL TRANSACTIONS.— C. 4^5 



material, (3) large surface area of sea in relation to depth, (4) disturbance by 

 wind. 



Other problems. 



Dr. W. K. Spencer, F.R.S.— 4. The Starfishes and Cystids. 

 These are not homogeneous faunas developing in their own areas, but 

 migratory faunas brought in at various times by various floodings. History 

 then can only be followed in relationship to larger considerations. 



1. Cambrian. — Only fragmentary ' Cystid ' remains are recorded from 

 Britain. Stromatocystis is found in Newfoundland and Bohemia suggesting 

 a trough connecting these areas. The Carpoids (a stock near akin to 

 ancestral starfish) are confined to Bohemia and Languedoc. 



2. Tremadoc. — New cystids and first starfish in Languedoc fauna, 

 Macrocystella (cystid) in Shropshire. 



3. Arenig. — Ramsay Island fauna. 



4. Llanvirn. — A rich and varied development from fauna (2) in Bohemia 

 (DjY) ; greater part of starfish fauna still archaic, also brittle stars with 

 true starfish ; carpoids and cystids. Only British echinoderm belonging 

 to the Bohemian-Languedoc fauna is a species of Palaura found in the 

 zone of Didymograptus bifidus (Upper Hope Shales of Shropshire). 



5. Caradoc-Bala Fauna. — Middle Ordovician of Chinese Turkestan has 

 the three species of Spy Wood Grit (early Caradoc) of West Shropshire 

 fauna and Stenaster also found in Wales. The Bala Cystids are also related 

 to those found in Asia. The genus Silur aster found in the Bala beds in 

 Wales and Shropshire has distinct relationships with the Bohemian DiY and 

 D3 faunas. The Bala fauna also has relationships with the Canadian and 

 Kentucky Trenton faunas. 



6. Starfish Bed, Girvan. — Rich Echinoderm fauna ; (a) Starfish are 

 related to those of Richmondian of Ohio Basin (and sorne Trenton forrns) 

 together with a new fauna. This combination later dominates the Silurian 

 and Devonian. The faunas are quite different from Welsh-Bohemian 

 fauna (5), the only Welsh-Bohemian-Central Asiatic elements are those 

 also found in the Trenton. (6) Cystid fauna has same two constituents, i.e. 

 American and a new fauna which is really an old fauna (2) as developed in 

 Languedoc. The number of peculiar genera common to both is very 

 remarkable. An explanation might be an Eastern reservoir sending migrants 

 by an Arctic route to Girvan. Starfish are not known from the con- 

 temporary Welsh, Irish or Bahic beds. Cystids in these three areas are as 

 a whole different from those of Girvan and have a common element, 

 apparently Baltic in origin. 



7. Wenlock of Pentland Hills shows fauna of aflnnities with Girvan (6) 

 together with new species from the north-east. Wenlock of Central England 

 brings in new forms related to contemporaneous American faunas, differing 

 from Scottish fauna. 



8. Ludlow of Leintwardine and Lake District has derivatives of Girvan (6), 

 suggesting that that fauna had moved southward, plus some elements related 

 to Languedoc (2). 



Afternoon. 



Excursion to Upware and Warboys. 



Saturday, August 20. 



Excursion to Thrapston and Stamford. 



