VI 



Preface. 



So here are the Author's Copies at last. Or let us 

 dignify them by the name of ' Author's Edition ' ; 

 for, though reprinted without textual change and with 

 the original pagination of the Geological Magazine, 

 they are supplemented by this Preface and by an 

 Index, and the Editor has most kindly allowed me to 

 have them technically republished. 



There is one change, duly noted in the Geological 

 A 1 'agazine for October, 191 5 (p. 478). The numbers 

 of the rays in the Text-figure on p. 260 of the 1915 

 volume were inserted in the wrong order (contra- 

 solar instead of solar), and that has been set right in 

 this edition. 



In preparing these papers, one of the most difficult 

 tasks, as also one of the most important, was the 

 attribution of each specimen to its precise horizon. 

 On this matter it is possible to add a few details. 



In reference to Edrioaster buchianus (Study II), 

 it had escaped me that in 1885 T. Ruddy (Proc. 

 Chester Soc. nat. Sci., Ill, p. 123) had written thus : 

 " Agelacrinus Buchianus (Forbes), Protaster Saltan 

 (Forbes), and one or two other species seen in other 

 collections from this neighbourhood, have been found 

 in Zones 8 and 9," that is to say in the zones which 

 Ruddy called those of " Strophomena expansa " and 

 " Orthis altemata ", just above the " Little Ash " of 

 the Geological Survey memoirs, at the base of the 

 Bala series. 



The horizon of Steganoblastus (Study V) was left 

 doubtful. Mr. Walter Billings, however, tells me 

 that the beds at Division Street, Ottawa, in which 

 the specimens were found, occupy the upper 20 feet 

 of the Trenton Limestone, as there exposed, and 

 yielded also examples of Archaeocrinus desiderattis, 

 Hybocrinns co/iicus, and Carabocriims sp. At 20 feet 

 from the summit Cyclocystoides and Aniygdalocystis 

 were found. I infer that Steganoblashis may have 



