FOSSIL REPTILES. 623 



There is a large broad plastron of abrlominal ribs which 

 occupies the whole of the front of the abdomen, from a little 

 behind the coracoid to the front of the pubis. The riblets are 

 all slender and arranged in series of threes — a long outer riblet, 

 a shortei- middle one, and a still shorter inner one. In front the 

 innermost series remain free, but on passing back they become 

 anchylosed into united groups of two, three, and four. There 

 are probably four seiies of riblets to each vertebra. Altogether 

 there are 31 groups of ribs. 



The pelvis is preserved in two specimens besides the type, and 

 every detail of its structure is known. The ilium is similar to 

 the type found in Belodon and Erythrosuchus. The acetabulum 

 is large, and closed, and the ilium has a well-marked supra- 

 acetabular ridge. The iliac crest is developed mvich more back- 

 wards than forwards, and the whole crest measures 28 mm. in 

 length. The pubis is comparatively short and broad. It forms 

 a complete symphysis with its neighbour, and the outer border, 

 which is considerably thickened, passes almost directly down- 

 wards. A very remarkable feature of the bone is the presence of 

 two pubic foi^amina. The upper one, which is apparently the 

 homologue of the normal pubic foramen, is the smaller of the two 

 and is fairly close to the acetabulum. The other is close to the 

 symphysis. In the type specimen both pubes are well preserved 

 and the foramina are exactly similar on both sides. The ischium 

 is a variety of the plate-like form, but long and slender. It has 

 a complete symphysis with the other ischium. 



The femur measures in the type 58 mm. : in a second specimen 

 55 mm. It has a slight double curve as in most reptilian femora. 

 The ends have been largely cartilaginous. On the inner and 

 posterior side, near the union of the upper and middle third, there 

 is a well-marked small trochanter. 



The tibia and fibula are not perfectly preserved in any of the 

 specimens, but in one or other both upper and lower parts are 

 shown. They are apparently a little shorter than the femur and 

 considerably more slender. 



The tarsus consists of two proximal elements, and probably 

 four distal tarsals. The astragalus is irregularly cubical, and the 

 calcaneum considerably broader than long. There appears to be 

 little in the way of a heel. Of the distal tarsals the 4th is the 

 only large one. 



The metatarsals are all well developed, and the 5th has the 

 peculiar Rhynchocephalian development. Of the others the 3rd is 

 the longest. The 4th is slightly longer than the 2nd, and the 2nd 

 considerably longer than the 1st. The 1st, 2nd, and 3rd digits 

 have well-developed claws, but the 4th has the phalanges rather 

 weak and the claw, if present, was very small. The 5th toe 

 also has a small claw, though larger than that of the 4th. The 

 digital formula is 2, 3, 4, 5, 3. 



Dermal ossifications are present along the back from the head 

 to at least well down the tail. These are arranged in pairs, one 



