vi PREFACE. 



on the Cretaceous Echinoderms ; but, alas ! his untimely and much-lamented death pre- 

 vented him from even commencing that work upon which his mind had been so long and 

 busily engaged, and which was looked forward to with so much interest by all who 

 knew the high qualifications of my friend for his selected task. But the mysterious decrees 

 of Providence disappointed our expectations, and at the same time deprived Natural Science, 

 in this country, of one of its brightest ornaments and warmest advocates. It would be 

 doing violence to my own feelings if I did not. on this occasion, record the high estimation 

 in which I held the opinions of my distinguished colleague on all points relating to the 

 work we had undertaken together, and the uniform deference I paid to his suggestions, as 

 to the best mode of executing the same, which were always dictated by that kindness, 

 frankness, and wisdom so characteristic of the man. 



Having been thus thrown entirely on my own resources, before the real difficulties 

 of the work began, I have experienced more than ever the deep responsibility of the 

 task I have undertaken. I trust the circumstances I have narrated will entitle me to 

 the consideration and indulgence of all who know the nature and amount of the 

 difficulties to be grappled with in a work like that in which I am engaged, and the 

 time and labour necessary to overcome them. I can only add, that I have spared neither 

 time, labour, nor research, in order to make this Monograph worthy of the confidence 

 originally reposed in me ; but how far I may have succeeded in my efforts, it remains for 

 others to decide. 



At the suggestion of my excellent friend, Thomas Davidson, Esq., author of the 

 magnificent Monograph on the Brachiopoda, and several other kind friends interested in 

 the success of this work, it was thought advisable that, at the conclusion of my Monograph 

 on the Oolitic species, I should proceed with the description of the Cretaceous forms, in 

 order that a greater unity in the arrangement and management of the subject might be 

 observed in the two Monographs on the Echinodermata of the Secondary rocks ; and a 

 proposal to this effect has been submitted to your Council, and received its sanction. 



I have ventured to propose some important alterations in the classification of the 

 Echinoidea, and have grouped the genera into thirteen natural families, many of which 

 are entirely new. My object has been to attain a more natural method, and thereby 

 facilitate the study of the different groups. I have given an analysis of these families at 

 the commencement of the work, and enumerated the most common types of each. 



In the description of the species, I have taken them in their stratigraphical order, 

 always commencing with the species found in the oldest rock in which the genus is 

 discovered, thus — a, Lias, Lower, Middle, and Upper ; b, Inferior Oolite ; c, Great Oolite, 

 including Pullers-earth, Stonesfield Slate, Great Oolite, Bradford Clay, Porest Marble, and 

 Gornbrash; d, Oxford Clay; e, Coralline Oolite, including Calcareous Grit, and Coral 

 Rag ; /, Kimmeridge Clay ; y, Portland Oolite ; h, Purbeck Beds ; — so that my work has 

 the double advantage of being stratigraphical and palaeontological at the same time, a 

 mode of treating the subject which I hope will prove useful and convenient to geologists. 



