WEALDEN PTERODACTYLES. 541 



tions given by the sockets in the portion of npper jaw of the Cretaceous Pterodacfylus 

 compressirostris. 



The dentary bone supporting the above-numbered teeth is slender and subcompressed ; 

 its depth is given in figs. 1, 2, and 4 (nat. size) ; its thickness is shown in fig. 3. 



This is the same at both upper and lower borders, which are similarly rounded off"; 

 it is less half way down, owing to the concavity, vertically, of the inner surface of the 

 ramus (ib., fig. 4). The outer surface (fig. 1) is nearly flat ; it is traversed lengthwise by 

 a linear impression, which is 5 m.m. below the upper border at the hind end of the pro- 

 portion of the ramus figured in fig. 1, and is 7 to 8 m.m. below the outlets of the 

 sockets of the teeth 7 — 9. This linear impression does not indicate a suture. 



The ramus slightly increases in thickness, with a gain of convexity externally and a 

 deeper concavity internally (both being in the vertical direction), at the fractured end 

 (ib., fig. 1, 32) nearest the symphysis. At the opi)osite end the angular element (ib., 

 fig. 4, 30) forms the inwardly prominent lower border ; the line between which and the 

 thin flat splenial forms (ib., ib., 31) is clearly sutural. 



The portion of the right dentary preserved (PI. II, figs. 2, 3) answers to that 

 containing the sockets of the teeth numbered 2 — 9 in fig. 1. There is the same 

 obscurity or lack of demonstration of a socket or tooth behind the socket 2. 



The bases of the teeth are preserved in the sockets (numbered 2 — 6), and partly 

 project from the sockets 2 and 3, but the sockets 7, S, 9, are vacant. 



The articular portion of the right ramus (figs. .5, 6, 7) lacks the prominent, backwardly 

 directed, end of the subangular (30)- 



The articular concavity (fig. 6, a) is transversely extended, chiefly by the production 

 of its inner wall (ib., h) ; its npper boundary is sinuous by a backward production of its 

 mid part ; the upper surface in advance of the cavity is smooth and gently convex across ; 

 it narrows to the ordinary thickness of the ramus about an inch and a half in advance of 

 the articulation. In this extent it shows no trace of a coronoid rising. The inner 

 surface is impressed with a deep longitudinal cavity (ib., fig. 7, c). 



According to the usual proportions of the upper and lower jaws of Pterodactyles, 

 the premaxillary of the present species must have been twice, or nearly twice, the depth 

 or vertical diameter of the portion of that bone of Pterodadylus compressirostris (figured 

 in Pter., PI. 3, fig. 8). Both upper and lower jaws of PterodactyJus sayittirostris must 

 have been broader, less compressed, than in the Cretaceous Ptcr. compressirostris. 



The value of a symphysis mandibuli, with its natural anterior termination, like that of 

 the Gault species {Pterodactylus Daviesii), is its demonstration of a character determinative 

 of the genus of Pterosaurian. Were it produced into a slender-pointed edentulous style, 

 or ' rostrum,' it would lead to a reference of the species to Von Meyer's genus Rampho- 

 rhyncJius and Family ' Sttdidirostres.'^ The opposite extreme is shown bj' the thick 



1 ' Palaeontographica,' Heft i, 4to, 1846. 



