AND MESOPLODON SOWEEBYI. 775 



part of the palate bone entered into the construction of the outer wall of the 

 nares. 



The basis cranii was concave, owing to the lateral elevations of the basi- 

 occipital. The occipital surface of the cranium was not so vertical as in cavi- 

 rostris, and had a faint mesial ridge. The foramen magnum was If inch high 

 by If inch wide. There was no trace of an interparietal, unless a small pro- 

 cess anchylosed to the supra-occipital, and projecting into the mesial part of 

 the frontal, could be thus considered. The ex-occipitals were prolonged exter- 

 nally into a jugal process, which was separated by a cleft from the lateral 

 elevation of the basi-occipital. 



The squamoso-zygomatic part of the temporal resembled the same bone in 

 cavirostris. Unfortunately, the mastoid and petro-tympanic elements of the 

 temporal had not been preserved in this specimen of Sowerbyi. Three canals 

 communicating with the cranial cavity opened into the periotic hollow. 



The parietal bone formed a large share of the floor and anterior wall of the 

 temporal fossa, and ascended between the occipital and frontal bones for 1\ 

 inch above the temporal crest. The relations of the frontal bone to the great 

 lateral crest of the cranium were similar to those described in cavirostris, but 

 at the summit of the skull, owing to the differences in size, shape, and direction 

 of the two nasals, the frontal passed forwards between the upper ends of the 

 two superior maxillae, and articulated not only with the nasal but with a 

 narrow process sent backwards from each pre-maxilla. The frontal formed also 

 the roof of the orbit, and possessed a pre- and post-orbital process. An optic 

 and a pre-optic foramen opened into the deeper part of the orbit. 



A small part only of the great wing of the sphenoid was visible on the 

 surface of the skull, and it contributed only in a minor degree to the formation 

 of the floor of the temporal fossa, which was chiefly composed of the parietal 

 and squamoso -temporal bones. The malar had the same relations as in cavi- 

 rostris, but the lachrymal was relatively larger than in that animal, for not only 

 did it assist in the formation of the roof of the orbit, but it extended so far out- 

 wards and forwards as to articulate with the pre-orbital process of the frontal, 

 and contributed to form the profile outline of the cranium. 



The lateral halves of the lower jaw were not anchylosed at the symphysis. 

 Both the upper and lower borders were concavo-convex, but the concavity on 

 the lower border was deeper and proportionally longer than in cavirostris, so 

 that the bone had a lighter and more elegant appearance. The upper border 

 possessed in its anterior half a dental groove, and a single large, triangular, 

 laterally compressed tooth was present on each side, only the curved and 

 backward directed apex of which projected beyond the socket. The slight pro- 

 jection of the teeth may, perhaps, be due not merely to the non-adult state of 

 the animal, but may indicate that it was of the female sex. The socket was 



VOL. XXVI. PART IV. 9 Q 



