PEOF. OWEN ON THE SKFLL OF AEGILLOENIS LONGIPENNIS. 23 



2. On the Skull of Argilloenis longipennis, Ow. By Professor 

 Owen, C.B., f.R.S., F.G.S., &c. (Eead November 5, 1879.) 



[Plate IL] 



I HATE been favoured by "W. H. Shrubsole, Esq., F.G.S., to whom 

 I was indebted for the humeral evidences of Argillornis hngipennis^\ 

 with a fossil from the same formation and locality (London Clay, 

 Sheppey), which, when cleared of matrix, has afforded the subject of 

 the following description. 



It is a considerable portion of the skull of a bird (PI. II.), 

 wanting the lower jaw and fore end of the upper jaw : some pro- 

 minent parts are abraded, exposing a pneumatic cellular structure. 



The length of the fossil is 5 inches 4 lines =135 millims. ; the 

 breadth across the lacrymals (fig. 2, 73) is 1 inch 9 lines = 45 millims. ; 

 across the mastoids (ib. s, s) 2 inches =50 millims. ; but these pro- 

 minences have suffered abrasion. 



The coalesced frontals (fig. 2, 11, 11'), which are 2 inches 6 lines = 

 63 millims. in length, have joined the prsemaxillo-nasals (fig. 2, 15-22) 

 by a transverse suture, 1 inch 2 lines =30 miUims. in length. 

 Posthumous pressure has driven this part of the frontal two or three 

 lines below such base of the upper mandible (fig. 1, 11, 22). 



Defining the hind part of the frontal by a faint linear trace of a 

 fronto -parietal suture, 7, the breadth of the bono is here 1 inch 

 6 lines =37 milhms. The whole of the preserved extent of the 

 frontal is smooth, devoid of intermuscular crest or ridges, feebly 

 convex behind the orbits, becoming as feebly concave transversely 

 between the orbits — this concavity expanding as the bone advances 

 and gains breadth, and the lateral surface becoming transversely 

 convex where the frontal, 11, joins the lacrymal, 73 (fig. 2). 



But a small proportion of the assumed parietal (fig. 2, 7) preserves 

 its outer surface, which is smooth and unimpressed. That of the 

 parieto-occipital, overarching the cerebellar prominence (fig. 5, 7-3) 

 with the mastoid protuberance, 8, present only on the left side, as 

 also that of the occipital boundary of the upper half of the occipital 

 foramen, 0, are represented by the remains of the cancellous struc- 

 ture. The basi- and paroccipitals are broken away. On the right 

 side is preserved the thin convex inner plate of the cranial Avail, 

 which protected the optic lobe (fig. 6, op). The breadth of the fora- 

 men magnum (fig. 5, 0) is 7 lines =15 millinas. The depth of the 

 cranium from the hind end of the frontal to the lower surface of the 

 basisphenoid is 1 inch G lines =39 millims. The base of the post- 

 orbital process, indicated on the right side (fig. 2, 12), and the cast 

 of the orbit in the matrix (fig. 1, 0), indicate the fore-and-aft 

 diameter of that cavity as about 1 inch 6 lines. The slender de- 

 scending process of the lacrymal (fig. 1, 73), 3 lines =6 millims. in 

 breadth, is convex across, concave vertically ; the upper expanded 

 * Quart. Journ. Geol. Soc. vol. xxxiv. 1878, p. 124, pi. vi. 



