ANNIVERSARY ADDRESS OF THE PRESIDENT. IxV 



particularly the case with the Balanidse or Sessile Cirripedes. Their 

 form depends greatly on their position and grouping. The surface 

 of attachment has a great eifect on the form of the shell ; for, as the 

 shells are added to at their bases, every portion has at one time been 

 in close contact with the supporting surface. Mr. Darwin observes, 

 that in consequence of the great variability of those features which 

 are generally considered as characteristic, he has been compelled for 

 the identification of species to have recourse to characters which 

 require the closest examination. Moreover, he considers that with- 

 out an examination of the opercular valves, it is seldom that the 

 Sessile Cirripedes can be satisfactorily determined in a fossil condi- 

 tion. The Balanidae do not appear to range lower down in the 

 geological series than the Eocene period, when both in Europe and in 

 America they were represented by few species ; although they abounded 

 during the Miocene and Pliocene periods. But owing to the diffi- 

 culty of identifying species the number of nominal species is far too 

 great. Mr. Darwin believes that, if properly examined, it would be 

 found that the whole number of species of Balani in the several ter- 

 tiary formations, from the Eocene to the Glacial, throughout Europe 

 would not exceed twenty. 



Mr. Sharpe's contribution to this volume is a portion of the con- 

 tinuation of his valuable monograph on the Fossil Remains of Mol- 

 lusca found in the Chalk of England. This portion is still confined to 

 the Cephalopoda, and contains the description of thirteen species 

 of Ammonites illustrated by six plates. 



The last and, to many geologists, perhaps the most interesting 

 contribution to this volume is the third part of Mr. F. Edwards's 

 monograph of the Eocene Mollusca, or descriptions of shells from the 

 older Tertiaries of England. In the two former parts Mr. Edwards 

 had described the Cephalopoda and the Pulmonata, or free air- 

 breathing Mollusca. This third part contains an account of the 

 Prosobranchiata, one of the two divisions into which M. Milne- 

 Edwards has subdivided the water-breathing Gasteropoda, the other 

 being the O'pisthohrancliiata. With reference ^o the dental appa- 

 ratus of the Gasteropoda, to which much attention has recently been 

 paid by many distinguished naturalists for the true identification of 

 genera, Mr. Edwards justly observes, that however valuable it may 

 prove to malacologists, it can only be indirectly available to the 

 palseontologist. The genera described in this part are Cyprcea eight 

 species ; Ovula one, problematical ; Marginella seven species ; Valuta 

 thirty-one, seven of which have been added by the author himself. 

 With regard to one of these, V. maga^ possibly the V. magoruniy 

 Sow., and figured imperfectly by Brocchi as a subapennine species, 

 Mr. Edwards observes that Prof. Beyrich has described a Volute 

 from Westeregeln, V. decora, Beyr., so closely resembling this 

 species that it is difficult to distinguish them. Should they on 

 actual comparison or further discoveries prove to belong to the same 

 species, Mr. Edwards observes that the name given by Prof. Beyrich 

 must supersede that given by himself. These genera are illustrated by 

 eight plates by Mr. J. de C. Sowerby. The next Part will commence 



