On some Reptilian Fossils from South Africa

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Abstract
T his subgenus is founded on four skulls, forming part of the collection transmitted to the British Museum in 1858, by His Excellency Governor Sir George Grey, K.C.B., from the sandstone rocks at the foot of the Rhenosterberg, S. Africa. These skulls belong, by their dentition, to the Dicynodont family, but present such strongly marked deviations from the type species of the genus ( Dicynodon lacerticeps , Ow.) as to indicate a distinct subgeneric section; they were accordingly entered in the Museum list, and labelled in the cabinet where they are exposed to view, under the term Ptychognathus . Dicynodon (Ptychognathus) declivis, Ow. (Plate I. figs. 3, 4, 5.) In this species, assuming the horizontality of the upper (fronto-parietal) plane of the cranium (P1. I. fig. 3 ll) as giving the natural position of the skull, the broad plane of the occiput meets the fronto-parietal plane at an acute angle, rising from the condyle upwards and backwards—a direction not hitherto observed in any reptile, and similar to that presented by the occiput in relation to the vertex in the feline and many other gyrencephalous mammals. The fronto-parietal plane (ib. fig. 5) is bounded by an anterior ridge, 14, 15, extending from one superorbital process to the other, with a gentle convexity forward, including the interorbital space. From this ridge the facial part of the skull (fig. 3 15, 22) descends in a straight line in a direction nearly parallel with that of the occiput, but slightly diverging from that parallel as it cxtends downward

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