778 MR. c. w. AXDEEWs ON A NEW uiitu [Juue 20, 



hemispherical, its upper border being very slightly flattened. The 

 foramen maipittm is relatively large and is subcircular, the lateral 

 and ventral borders being slightly flattened. Above the foramen 

 there is a well-marked cerebellar prominence (c6.j).) from which 

 the bone has been almost entirely broken away. On either side 

 of the prominence, about 4 mm. above the foramen nia;fnum, is a 

 small vascular foramen from which a groove runs downward and 

 outwards to the base of the paroccipital \:)rGcesH(p.p.). These pro- 

 cesses are large and convex from above downwards ; their rounded 

 outer extremities do not extend below the level of the foramen 

 magnum and their ventral border is continuous with the supra- 

 foraminal ridge. Beneath the paroccipital processes the occipital 

 surface is flattened and is produced downward beneath the 

 occipital condyle in a pair of prominences, the extremities of which 

 form the mammillary tuberosities {m.t.). About on the level of 

 the occipital condyle there are several foramina (transmitting 

 the hypoglossal, pueumogastric, and glossopharyngeal nerves, 

 and ? carotid artery). 



The lambdoidal ridge, which forms the dorsal border of the 

 occipital surface, is much worn away, but probablj^ was never very 

 strongly marked : near its lower end it joins the ridge forming the 

 outer border of the paroccipital process and then runs forward on 

 to the zygomatic process. This projects strongly forward towards 

 the postorbital process (p.o.p.), from Avhich it is separated by a space 

 of about 6 mm. only. The temporal fossa (tf.) is very deep and 

 well-detined ; it extends scarcely at all on to the roof of the skull. 

 The temporal ridge joins the lambdoidal crest near its outer end 

 and then passes forward and inward : anteriorly it passes on to the 

 postorbital process, along the middle of which it runs and at the 

 tip of which it terminates. The parietal region of the skull 

 between the temporal fossae is only very slightly convex, but in the 

 frontal region between the postorbital processes the convexity is 

 greater, and there is a pair of slight prominences separated in the 

 middle line by a shallow depression which broadens out till in 

 the interorbital region the whole roof of the skull is slightly concave 

 from side to side. The orbital borders of the frontals are thin, 

 sharp, and slightly upturned, but in front of the orbits the edges of 

 the skull-roof become thickened and form a broad surface for union 

 with the lachrymals (l.s.), which unfortunately are both wanting in 

 this specimen. The region between the lachrymals is somewhat 

 swollen, slightly convex from side to side and strongly so from before 

 backward ; this inflated region terminates anteriorly in a deep trans- 

 verse groove, the so-called naso-frontal hinge (r.h.). As a matter 

 of fact this groove does not occur at the j miction of the nasals and 

 frontals, at least in Phaethon, to which the present species is most 

 nearly allied. In the skull of a young individual of P. cetliereus 

 described by Mr. W. P. Pycraft, the groove divides the nasals into a 

 posterior inflated portion and an anterior region cleft by the nares 

 and separated one from another by the facial processes of the pre- 

 maxilljE ; it will therefore be better to speak of this hinge as 

 " rostral " iustead of frouto-nasal. 



