4«S4 Geohxjical Society. 



tt) Spirift'yiiio include two t^'pcs characterized b}' external diffe- 

 rences. Of these two type.s, one, in \\liieli there are niinierous 

 rihs and a relatively-large rounded fold and sinus, is relegated to a 

 new genus ; while the members of the other ty])e, which include 

 shells with a few large angular ribs, are for .the jjresent retained in 

 >:ipi)-ifrriua, although the ty])e-sj)eeies of that genus was derived 

 from the Lias. The subdivision here suggested for the C'arbonifcit.ns 

 forms will, it is believed, prove to be ajiplicable to the later sjxjeies 

 also. 



2. 'Jurassic Chronology: I — Lias. Supplement 1, West 

 England Strata.' liy S. " S. Buckman, F.Cl.S. (Kead, in tie 

 absence of the Author, by Dr. W. D. Lang, M.A., F.G.S.) 



In this communication the following points are discussed : — 



(1) The Ammonite and some Brachiopod faunas of the Lias of 

 Gloucestershire and Worcestershire. 



(2) A method of faunal plotting as an aid to faunal analysis. 



(3) That in the collection, analysis, and comparison of faunas, 

 the following causes of failure have to be considered : — Stratal, 

 Depositional, Faunal, Dispersal, Exposure, Collection, Arrangement, 

 Nomenclature, Fossilizatioii, Preservation, Extraction, ZonalizatiiiU, 

 I'ublication ; but several of these are not applicable to results 

 derived from the investigation of limited areas. 



(4) The evidence appears not only to support the conclusions of 

 the Author's former paper, but to show that in certain cases a 

 fuller sequence of faunal episodes may be required. 



(5) The fauna of small Ammonites in these Liassic beds, 

 especially that of small Schlof/iei/m'ce at Gloucester, suggests 

 comparison with the faunas of Hierlatz and Spezia. The use of 

 technical terms for different sizes of organisms, especially for small 

 forms, is briefly illustrated. 



(6) It is suggested that the strata and faunas of these Conti- 

 nental localities are not so exceptional as they appear to be at first 

 sight ; and that English localities may be studied with advantage, 

 in comparison witli and explanation of the features of these 

 Continental deposits. 



(7) It is found that the preserved strata of the Gloucestei'shire- 

 Worcestershire Lias under consideration happen in the main to be 

 deposits of dates when the living Ammonites were rather small ; 

 while there is faunal failure and presumably stratal failure of the 

 times when large Ammonites llourished. The converse phenomena 

 are mainly illustrated by North-Somerset deposits. 



(8) The times when large and small Ammonites lived appear to 

 follow one another like waves, illustrated even in a short table of 

 Liassic deposits. 



(9) As ;i result of the investigations connected with this paper 

 it seems to be advisable, for recording purposes at any rate, to make 

 further subdivisions in the scheme set forth in the Author's former 

 p.iper. 



