26 PKOP. p. M. DUNCAN AND ME. W. P. SLADEN ON" 



Fewkes, Garman, and Colton ; and every one of us wlio is inter- 

 ested in the subject, will remember tliat a species was traced 

 during the stages of its early growth, from the Pluteus to the 

 young perfect form, by Johannes Miiller, the father of this kind 

 of research, in 1855. 



The classificatory studies of the family, the descriptions of the 

 species, and the arguments regarding the affinities of the forms, 

 and the necessary limitation of the family to certain genera, 

 have occupied the attention of especially Desmoulius, Grray, 

 Desor, E. Forbes, Blainville, L. Agassiz, Aradas, Sars, Delle 

 Chiaje, Verrill, A. Agassiz, Liitken, and Troschel. We owe some 

 important morphological studies to Loven, and also to A. Agassiz 

 and Troschel. 



The ' E-evision of the Echini ' by A. Agassiz contains, besides 

 the synonymy of the species of the genera of the family, the 

 history of the successive writings on the group, and the argu- 

 ments regarding the propriety of extending the family so as to 

 include the genera Coelopleurus and Podocidaris, and also very 

 careful descriptions and drawings of the more important parts 

 of the species. 



The value of these researches by A. Agassiz is enhanced by 

 his subsequent writings in the Eeport on the Echinoidea of the 

 ' Challenger ' Expedition, and in his Report on the dredgings of 

 the U. S. Steamer ' Blake.' The delineations of Arhacia nigra 

 (Molina, sp.) by Loven in his ' Etudes sur les Echinoi'dees,' and 

 those of the species of Arhacia, Coelopleurus, and Podocidaris by 

 A. Agassiz, leave little to be desired. 



In 1883 we were describing the Tertiary Echinoidea of Kachh 

 and Kattywar for the ' Palseontologia Indica,' and we had the 

 opportunity of studying excellent specimens of species from two 

 geological horizons, namely the Oligocene and Miocene. Subse- 

 quently we extended our work, and have completed the description 

 of the Echinoidea of Sind. 



"We have thus been enabled to study several points in the 

 morphology of the test of four species of Ccelopleurus ; and the 

 result led us to examine the recent species of Coelopleurus from 

 the seas to the east of Africa. Owing to the kindness of Dr. 

 Giinther, F.E.S.,we have been enabled to examine the specimens 

 of Coelopleurus Maillardi, A. Agassiz, in the National Collection, 

 and to compare their structures with those of the fossil forms. 

 Pursuing our investigations, we studied the test of the species 



