ON THE SKULL OF NYCTODACTYLUS S 2 7 



palatal surface, it is so indissolubly united with the maxillae, pal- 

 atines, and premaxillary that no signs of its union can be detected. 

 One thing is certain, it does not separate the narial vacuities, 

 and in all probability it does not touch the pterygoid at all. 



Mandibles. — The mandibles are preserved nearly complete, 

 their tip only being wanting — the portion which led to the 

 detection of the specimen as it protruded from the chalk. It 

 was lying horizontally, with the under surface uppermost, but has 

 been entirely removed from the matrix. It has suffered a slight 

 lateral compression to the left. 



The cotylar cavity fits well on the condyles of the quadrate. 

 The projection back of the articulation is very slight, less so than 

 in Ornitliostoma. The rami are slender, flattened from within 

 outward, and are broadest at about their middle, the upper thin 

 margin being gently convex from near the cotylus to as far for- 

 ward as the symphysis, which begins about fifty millimeters in 

 advance of the anterior end of the external nares. From the 

 beginning of this symphysis, diminishing in width to the anterior 

 extremity, the under margin is convex, not carinated. About 

 twenty-five millimeters back of the true symphysis of the denta- 

 ries there is a symphysis of the thin bone which forms the floor 

 of the mouth. This forms a thin, deeply curved hind border 

 joining rami about midway between their upper and lower mar- 

 gins. The floor of the mouth from here onward seems to have 

 been, like the opposing palatine surface, smooth, and nearly 

 plane. The space between these surfaces, was, however, some- 

 what greater posteriorly than anteriorly, since the alveolar para- 

 pet is considerably deeper posteriorly. The concave posterior 

 margin of the floor is about twenty millimeters in front of the 

 anterior end of the internal narial vacuity. Anteriorly the mar- 

 gins of the mandibles are as in the upper jaws. In cross-section 

 through the symphysis the mandible was, I think, somewhat con- 

 cave or partly plane on the sides, with the under margin convex, 

 not convex throughout, as I have thought might be the case in 

 Ornitliostoma. The mandible certainly could not have possessed 

 very great strength in seizing. 



