vi PREFACE. 



labour. Amongst my foreign friends I reckon some who gave early attention to the 

 Triassic Ustheria minuta, especially the late much lamented H. G. Bronn, the veteran E. 

 von Alberti, and Naumann, as well as Geinitz, Beinert, Dunker, E. Sandberger, Oppel, 

 Krantz, Hassencamp, Daubree, Schimper, Engelbardt, E. d'Eichwald, Pander, G. von 

 Helraersen, C. M. Wheatley of Pennsylvania, and W. B. Rogers of Boston, whose 

 brother, Professor H. D. Rogers (Glasgow) has also eminently aided me. The late Mr. 

 P. Duff, Dr. Mantell, and Prof. Quekett, Dr. W. Baird, Sir C. Lyell, Sir R. I. Murchison, 

 the Rev. Messrs. Symonds, Brodie, Hislop, Austen, and Eisher, Dr. Oldham, Prof. Morris, 

 Mr. Binney, Mr. G, Tate, Mr. Salter, Mr. Peach, Mr. J. Miller, Prof. W. C. WiUiamson, 

 Messrs. 8. P. and H. Woodward, Mr. D. Forbes, Mr. Rofe, Mr. Grossart, Dr. Rankine, 

 Mr. Leckenby, Mr. Bean, Prof. Tennant, Mr. E. Hull, Mr. Etheridge, Mr. Kirshaw, 

 Mr. C. Moore, Mr. Beckles, Dr. T. Wright, Mr. J. Plant, Mr. G. E. Roberts, Mr. C. E. 

 Austin, and Mr. H. Seeley, must be enumerated as sources either of material or infor- 

 mation for this Monograph ; and my friend, Mr. G. West, must be especially thanked 

 for the patient care bestowed on the drawings, and for the great skill with which he has 

 helped me most materially in unravelling many obscure points of structure. 



Some of the best and rarest of the specimens illustrated in this Monograph are in 

 the British Museum, the Museum of the Geological Society, and that of the Geological 

 Survey : to the officers of these Museums my thanks are especially due. 



To render the history of Estheria as complete as circumstances permit, I have described, 

 in an Appendix, those other fossil bivalved Entomostraca that are in direct association 

 with the Estheria, — that is, occurring in the same strata. I hoped that they might throw 

 additional light on the habitats of the ancient Ustheria ; the results, however, are not 

 conclusive ; but will probably be found useful. 



