JtCVlll PEOCEEDINGS OF THE GEOLOGICAL SOCIETY, 



cies wliich are common to the Silurian, Devonian, Carboniferous, 

 and Permian systems, which will be treated of in the concluding 

 portion of his Monograph, He then proceeds to describe the fol- 

 lowing species : — Terehratula, 4 ; JRensselceria, 1 ; String ocephalus, 

 1 ; Athyris, 4 : Merista, 1 ; Metzia, 1 ; TJoicites, 1 ; Spirifera, 14 ; 

 Spiriferina, 2 ; Gystina, 3 ; and Atrypa, 3 ; several of which are 

 now for the first time added to the British lists. They are illus- 

 trated by nine plates, all of which have been drawn on stone by 

 Mr. Davidson himself, a fact which adds materially to their value, 

 by vouching for their correctness. Por when an author who has 

 himself described the species is also able to figure them on stone, 

 we are sure of having those typical features brought ovit which 

 might escape the notice of the professional draftsman, who is not 

 enough of a conchologist to seize upon the characteristic points. 



The next Monograph is by Mr. Searles "Wood, on the Bivalves 

 of the Eocene Mollusca. I must here remind you that the illus- 

 tration of the Eocene Mollusca was originally undertaken by Mr. 

 E, E. EdAvards, who had commenced with the Univalves, and had 

 already published three parts, with thirty-three plates. When, 

 however, the state of his health prevented Mr. Edwards from 

 going on with his work, Mr. Searles "Wood, sensibly alive to the 

 disappointment felt by many Palseontologists who were anxiously 

 looking to the completion of this important Monograph, undertook 

 the task himself. Hoping, however, that Mr. Edwards might in 

 time be able to resume his work on the Univalves, Mr. S. AVood 

 began with the Bivalves, which was commenced in the volume for 

 1859, with thirteen plates. In the present volume he has given 

 us seven plates, with an accurate description of the following 

 species : — Jfodiola, 5 ; Area, 18 ; Cucullcea, 1 ; Pectimctdus, 10 ; 

 Limopsis, 2 ; TrigonoccBlia, 2 ; Niicula, 23 ; Leda, 9 ; and JJnio, 7 ; 

 of which a very considerable number are new species. 



The last Avork in this volume is by Professor Owen, and con- 

 sists of Supplements II. & III. to his Monograph of the fossil 

 Reptilia of the Cretaceous formations, with ten plates. The first 

 Supplement (No. II.) contains descriptions and additional par- 

 ticulars oi Plesiosmirus planus, Owen; PI. Pernor di, Owen; PI. 

 Neocomiensis, Campiche, and PI. latispinus, Oweu. The second 

 Supplement (No. III.) gives an account of the left ramus of the 

 lower jaw of a young Iguanodon from Brixton, Isle of Wight, 

 including the entire series of alveoli, fifteen in number. Erom 

 a comparison of this jaw with those of larger specimens, of greater 

 length, and with a greater number of alveoli, Professor Owen draws 

 this interesting conclusion, that the Iguanodon possessed the mam- 

 malian character of increasing the number of teeth and sockets 

 longitudinally, according to its age, like the true molars of mam- 

 mals, in new and distinct alveoli, behind those in place ; whereas 

 in the Crocodiles and other existing reptiles the number of teeth 

 and sockets does not vary with age, thus showing the greater 

 afiinity of the Iguanodon to the warm-blooded mammalia. 

 ■ I will merely add one remark, which I trust geologists will 



