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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 11, 



Figs. 1-6. Plaffiaidax Becklesii {^gs. 1-5), and Hypsiprymyius Gai- 

 mardi (fig. 6). Figs. 1 &4 show the entire right ramus of the 

 Lower Jaw^ in two pieces, on reversed slabs of the same piece of 

 matrix. (Magnified two diameters.) 



2. 3. 



[Figs. 1 & 4 represent the same right ramus of the lower jaw seen on the opposite surfaces of 

 a split stone, the two taken together affording data for a complete restoration of the jaw.] 



Fig. 1. a, b, e'. Outer side of the anterior portion of the right ramus of lower jaw; magnified 

 two diameters, a, b, outer side, b, o', d' e', impression of inner side. 



a. Incisor. 



b, c. Line of vertical fracture behind the premolars. 

 d'. Impression in the matrix of the condyle. 



e'. Impression of top of coronoid process. 



n'. Broken-off inflected fold of inner margin buried in the matrix. 



m. Place of the two molars. 



pm. Three premolars, the third or last divided by a crack. 

 Fig. 2. /. Section of the anterior piece of the jaw at the fracture b, c; x, inner surface ; y, outer. 



The notch at the top is formed by one of the sockets of the double-fanged true molar. 

 Fig. 3. g. Section of the hinder piece near b, c; x, inner surface ; y, outer surface. 

 Fig. 4. a', d. Inner side of the posterior portion of the same lower jaw on the opposite slab of 

 stone; b, d, e, inner side; b, a', h, cast and impression of outer side. 



a! , Outline of the incisor restored. 



b, c. Line of vertical fracture. 



d. Condyle. 



€, Coronoid process*. 



h. Impression of the three premolars on the matrix. 



i. Empty sockets of the two true molars. 



n. Orifice of dentary canal. 



o. Indication of the raised and inflected fold of the posterior inner margin. 

 Fig. 5. A". Third or largest premolar, showing the seven diagonal grooves ; magnified 54 dia- 

 meters. 

 Fig. 6. I. Corresponding premolar in the recent Australian Hypsiprymnus Gaimardi, showing 

 the seven vertical grooves ; magnified 34 diameters. 



[These illustrations Lave been obligingly lent by John Murray, Esq., F,G.S.] 



* The artist has made the point of the coronoid (e) project too much back- 

 wards, and the curve of the posterior margin too great; the line being nearly 

 vertical in the original. The projection of the condyle behind the coronoid mar- 

 gin is more considerable than is shown by the figure, and the neck longer. 



