6 



is a massive plate, the ends of which are produced in opposite directions ; 

 the one into a massive shorter prominence ; the other longer and plate-like. 

 Between these prolongations, the inferior edge of the bone bears a single 

 row of well developed teeth. The patch of small teeth first described, 

 commences at the extremity from which the longest process rises on the 

 opposite side of the series of large teeth. This Z-shaped bone is, from its 

 massive character, generally preserved, and I was long familiar with it, 

 before I could refer it to its position. In one specimen, a part of it bearing 

 teeth, adheres to the upper jaw at the diastema. 



The posterior part of the skull of one of the specimens above mentioned 

 displays typical reptilian characters. The occipital condyle is not perforated, 

 nor divided by sutures. The exoccipital bones project well backwards. 

 The lateral walls of the brain-case are massive as far forward as the exit 

 of the fifth pair of nerves ; anterior to this point they were thin or want- 

 ing. The basisphenoid carries two parallel descending laminae, which 

 bound a deep median fissure, and then unite anteriorly. Posteriorly they 

 abut on a descending process, which is followed by a lid-like element 

 which is applied to a, circular fossa with a raised border near the occipital 

 condyle. 



The articular face of the articular bone of the mandible consists of two 

 parallel cotyli, divided by a ridge of articular surface. This part of the 

 jaw is much depressed, as in Eryups. The large teeth of the lower jaw are 

 at the anterior extremity. 



The neural spine of the axis is flat and elongate antero -posteriorly. 

 From this point the neural spines rise rapidly in elevation until on the 

 dorsal region they are many times as long as the diameters of the centra. 

 The latter are not very unequal in their proportions in different parts of the 

 column. Those from the posterior regions are less compressed than the 

 dorsals and cervicals. The dorsals are separated by intercentra below, 

 which are small in the D. incisivus, and larger in the 1). gigas. All the 

 ribs are two-headed, commencing with the axis. All the crevical and dor- 

 sal vertebras have diapophyses with tubercular facets. The head of the 

 rib is prolonged downwards and forwards to the prominent border of the 

 anterior articular face, against which it abuts, but so far as yet observed, 

 without a corresponding facet. On the caudal vertebrae the two facets of 

 the ribs are approximated and finally are not distinguished. They are here 

 coossified with the centra. 



The humerus accompanying one of the specimens of D. incisivus, is of 

 the form No. 3, of my description of humeri in the Paleontological Bulle- 

 tin No. 29, p. 528. The extremities are expanded and the shaft is without 

 diagonal ridge ; the supracondylar foramen is enclosed, and the condyles are 

 robust. The pelvis of the D. gigas is in general like that of Glepsydrops nalali? 

 (I.e., p. 510 j. The elements are coossified, buttheischiopubic symphysis is not 

 so deep as in the Batrachia of the same beds. The ilium is shortened above, 

 and its direction is at right angles to the long axis of the inferior elements 

 The foramen of the internal femoral artery is distinct. The femur of the 



