CRETACEOUS FORMATIONS. 3 



pressed by a very shallow and wide, longitudinal or vertical channel; but this is 

 scarcely marked in a second specimen of a muzzle of the same species. In both 

 specimens the outer surface of the flattened part is less smooth than at the sides 

 of the muzzle, being impressed by numerous irregular, linear grooves, seemingly 

 vascular, affecting the vertical direction at the upper part, and the transverse 

 direction at the rest of the surface. 



The ridge where the two sides of the muzzle meet, above and beyond the 

 flattened surface, is more obtuse and is relatively thicker than in Plerodactylus 

 Sedgwickii. Were the same curve to be continued from the part of the ridge 

 preserved until it became horizontal, the vertical diameter of the skull at this part 

 would be not less than three inches ; it may, however, have risen to a greater 

 height, for the contour is not regularly curved, but sub-angular, as shown 

 in figs. 1 and 2. 



The facial part of the skull must have been narrow in proportion to its height, 

 and, no doubt, also to its length. The broadest part of the present fragment does 

 not exceed one inch and a quarter at the fourth pair of sockets; the adherent 

 matrix ( m , m, figs. 4 and 5) gives a seeming greater breadth to this part of the skull. 



The sockets of the first pair of teeth (a) are three lines apart, the interspace 

 equalling the largest diameter of the socket ; the bone forming this anterior 

 termination of the palate projects as a convexity below the level of the 

 alveolar openings, the plane of which is a little inclined outwards. This incli- 

 nation is increased in those of the second pair of sockets, which are nearly double 

 the size of the first, and are five lines apart. The second is separated from the 

 first socket by an interval of two lines ; its outlet has a full, oval form. The third 

 socket is four lines distant from the second, and exhibits the same ratio of 

 increase of size ; there is a shallow, vertical depression on the outer alveolar wall, 

 between the second and third tooth, the socket of the latter appearing to have made 

 a slight prominence on that part of the jaw. The palate at the interspace between 

 the second and third pairs of sockets is flat, showing no trace of the median ridge 

 characterising that part of the upper jaw, or of the groove at the corresponding 

 part of the lower jaw, in the Plerodactylus Sedgwickii. 



The upper jaw of the Plerodactylus simus, in the present specimen, has been 

 partially fractured across the third pair of sockets (figs. 1, 2, 5, c ), of which 

 only the forepart of the left one is here preserved, showing well-marked 

 vascular grooves. Its outlet, from this fracture, appears to be of a larger oval 

 or ellipse than in the second socket. 



The fourth socket (d) is preserved only on the right side, with about the right 

 half of the corresponding part of the bony palate. The outlet of this socket 

 resembles in shape and size that of the second ; it is three lines distant from the 

 third socket. 



