401 MR. K. W. HOOLEY ON THE [Julie I9I3, 



■both are wedged into the edge of the sternal plate in such a 

 manner that they cannot move farther in an inward direction. 

 Moreover, the articular surface is not produced beyond them, 

 • and thus absolutely prevents an inward, rotating movement past 

 ■the keel. The only motion possible is an outward one, the sternal 

 end of the coracoid sliding along in the articular groove, which 

 .'has projecting edges to keep it in position. In 0. latidens the 

 mechanism is very different from that observed in Ardea einerea. 

 -In lieu of an articulation in a straight line directed obliquely on 

 the anterior margin of the sternal plate, we observe a 

 semicircular free surface permitting an extraordinary rotatory 

 movement of the coracoids around the anterior edge of the 

 keel on to its sides; also it was possible for the sternal ends of 

 the coracoids to decussate completely, and not, as in herons, only 

 ;the inner third of the articular surface, which does not extend the 

 'full width of the bone. Dr. Plieninger * well shows how uncertain 

 lias been the knowledge of the exact position of the coracoid 

 articulations; he points out that Goldfuss located them in two 

 .little fossa? on the dorsal side of the sternum, and H. von Meyer, in 

 Pterodactylus, in a similar place, on the ground of the position of the 

 coracoids. In Oniitlwstomcr and in Nyctosaurus 3 Prof. Williston 

 says that they ' look dorsad and laterad.' The anterior process in 

 both these genera projects in front of the sternum, and, being very 

 close to that characteristic of the RhcvmphorTiynchus type, is there- 

 fore far removed from that of 0. latidens. In the examples of the 

 sternum from the Cambridge Greensand described by Seeley, the 

 anterior outline of the anterior process is directed obliquely forward 

 from the lateral expansions, not vertically as in 0. latidens ; and 

 the form and position of the coracoid facets differ. Dr. Plieninger 4 

 has well described the form of the sternum of both long- and 

 short-tailed forms. It is quite evident from my description and 

 the figures (PI. XL, figs. 3, 4, & 5) of 0. latidens that it is 

 impossible to include it within either of these two types. In the 

 type-specimen of Scaphognathus crassirostris ° the form of the 

 sternum cannot be accurately determined, as it is lying under the 

 flattened skeleton, and the aspect is therefore probably the dorsal. 

 According to Hermann von Meyer, . the sternum appears as a 

 broad rhomboidal shield with rounded ends. The sternum is not 

 known in Scaphognathus purdoni or Dimorphodon. 



All the specimens of other genera, where the sternum is well 

 displayed, can be assigned without doubt either to the long- or to 

 the short-tailed forms. 



1 ' Pterosaur, d. Jura Schwabens' Palaaontographica, vol. liii (1907) p. 299. 



2 'Restoration of Omithostoma (Pteranodon)' Kansas Univ. Quart, ser. A, 

 vol. vi (1897) p. 42. 



3 ' Osteology of Xi/c/osauncs (Nyctodactylus), &c.' Field Col. Mus. Publ. 78, 

 Geol. Ser. vol. ii. No. 3 (1903) p. 139. 



4 Op. supra cit. p. 298. 



5 A. Grjldfuss, Nova Acta Acad. Leopold. -Carol, vol. sv (1831) pt. 1, pis. vii 

 & "vi ii. 



' Eeptilien aus deni Lithogr. Schiefer d. Jura ' 1860, p. 43. 



