HYPSODON ETC. FROM BRITISH CRETACEOUS STRATA. 511 



Portheus Daviesii, n. sp. PI. XXII. fig. 13. 



This species is founded upon a specimen in the British Museum 

 from the Lower Chalk near Maidstone (?). It consists of a 

 right maxilla with the outer surface and teeth in a remarkably 

 good state of preservation, but wanting the posterior extremity. 

 Upon the same block of chalk there is a vertebra and a rod-like 

 bone with a falcate extremity, which may, perhaps, be a post- 

 clavicle. 



This maxilla has proportionally a greater vertical thickness than 

 has that of either of the species of Portheus described by Prof. Cope 

 or mentioned in this communication. The upper margin is slightly 

 convex from before backwards, and posteriorly has a well-marked 

 groove. The lower or dentary margin is strongly and regularly 

 convex ; in its present condition it is provided with twelve straight 

 teeth ; the anterior three are small, the median one rather larger, 

 and the remaining eight intermediate in size. The spaces ob- 

 servable between some of these are occupied by alveoli, and may 

 have borne teeth when the jaw was perfect. If such was the case, 

 then so much of the maxilla as is preserved may have possessed 

 fifteen or sixteen teeth ; at present there are twelve in situ. An- 

 teriorly the bone presents a very rugose surface for articulation with 

 the prsemaxilla. The piece of bone attached to the upper portion of 

 this surface is probably no part of the prsemaxilla, although occu- 

 pying its position. The space between the posterior margin of the 

 premaxillary articulation and the first maxillary tooth, shown in 

 figure 13, appears to have been naturally edentulous. The outer 

 surface is flattened and marked by ramifying vascular channels, 

 which pass in a backward and downward direction from foramina 

 situated towards the anterior part of the bone. 



This maxilla differs from those of all other species of this genus 

 at present known, in its proportionally greater vertical thickness, in 

 the convexity of the dentary margin, and also in the more uniform 

 size of its teeth. In this last character some approach is made to 

 the genus Iclitlujodectes ; but the larger size of the middle tooth 

 seems rather to ally it to Portheus ; and in the absence of the prse- 

 maxilla, by which its affinities could be more definitely determined, 

 it is thought best to place it in the latter genus. 



The vertebra, imbedded in the same block, is deeply biconcave ; 

 and the sides present large cavities, similar to those in the vertebree 

 of other species of Portheus. 



The rod-like bone has not the character of a rib, nor the ap- 

 pearance of a pectoral spine ; but it is quite possible that it may be 

 a ventral spine or a postclavicular bone. 



The specific name proposed for this specimen is intended as a mark 

 of respect for my friend Mr. "W. Davies, of the Palaeontological De- 

 partment in the British Museum, to whom I am indebted for the 

 kind manner in which he has facilitated my examination of the 

 specimens in the national collection. 



