360 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 22, 



DESCRIPTIONS OF PLATES XI. & XII. 



[The figures are all drawn on the scale of one-third of the natural size.] 



PLATE XI. 



Fig. 1. Mastodon {Tetralophodoii) longirostris, Kaup, from Eppelsheim : plan- 

 view of the penultimate true molar from the left side of the upper jaw. 

 a, anterior talon ; t, posterior talon ; b, c, d, e, the four principal ridges 

 which compose the crowns of the " intermediate molars " in the Tetra- 

 lophodons. An irregular longitudinal cleft along the middle divides 

 the crown into an inner and outer division. 



Fig. 2. The same tooth, seen in profile. 



[From a cast in tl^e Society's Collection.] 



Fig. 3. Mastodon {Tritoj)hodon) angustidens, from the Dep. Gers, in the Sub- 

 pyrenees : plan-view of the penultimate true inolar from the left side of 

 the upper jaw, showing the worn disks of the three principal ridges 

 which compose the crowns of the " intermediate molars: " in the Trilo- 

 phodons. a, anterior talon ; /, posterior talon ; b, c, d, the three ridges. 

 The longitudinal cleft is partially worn out. 



Fig. 4. The same tooth, seen in profile. 



[From a specimen in the Collection of M. Lartet, For. iNIem. G. S., Sei>san, 

 Gers.] 



PLATE XII. 

 [The letters to the figures refer to the same parts as in fig. 1, PI, XL] 



Fig. 1. Mastodon (Tetralophodon) Arvemensis, from Ramsey, near Harwich : 

 plan-view of the germ of the penultimate true molar from the right 

 side of the upper jaw. 

 Fig. 2. The same tooth, seen in profile. A large flanking mammilla is seen to 

 occupy the middle of each valley. 

 [This specimen is in the Collection of the Rev. J. R. Marsden, Great Oak- 

 ley, Essex.] 

 Fig. 3. Mastodon {Tetralophodon) Arvernensis, from SuflTolk : plan-view of the 

 germ of the last true molar from the left side of the lower jaw. 

 b, c, d, e,f, the five ridges composing the crown, the mammillae of which 

 are disposed alternately. 

 Fig. 4. The same tooth, seen in profile. 



[Figs. 3 & 4 are drawn from a cast in the Society's Museum ; the " bour- 

 relet " being partly restored from a Crag molar of similar age, also in the 

 Society's Collection.] 



April 22, 1857. 



Thomas Alfred Yarrow, Esq., C.E., Gresham House, Old Broad 

 Street, was elected a Fellow. 



The following communications were read : — 



1. Description of a New Fossil Crustacean (Tropifer Isevis, 

 C. Gould) from the Lias Bone- bed. Bv Charles Gould, 

 Esq., B.A. 



[Communicated by J. W. Salter, Esq., F.G.S.] 



Crustacean remains from this Bone-bed, and indeed from the Lias 

 itself, are so rare, that I feel no apologiy is necessary for introducing 



