1906.] 



DIAPTOSAUEIAN REPTILE. 



599 



iSphenodon, hilt the imperforate condition of the coracoid is a feature 

 found in a few Diaptosaurians. 



The pelvis is not much modified fi-om the type found in most 

 Diaptosaurians. The plate-like pubis and ischium are found in 

 Rhynchosaui'us. In the Phytosaur Erythrosuchus the pelvis is 

 very similar in structure ; in Sphenodon the pelvic structure is very 

 different. 



It is impossible to compare the tarsus with that of most allied 

 forms, as little is known of the tarsus in the Gnathodonts or 

 Phytosaurs. There is, however, an undoubted resemblance 

 between the tarsus of Iloioesia and that of Sphenodon, and this is 

 more marked when that of the embryo is considered. The 

 similarity is so close, that it is difficult to doubt that it indicates a 

 relationship. In ProcolopJion we also see some affinity. It is 

 interesting to note the similarity of the mode of articulation of 

 the 5th metatarsa\ 



Taking the various points into consideration, I conclude that 

 Howesia is a very slightly specialised Gnathod ont . It seems to show, 

 moreover, that the Gnathodonts are not true Rhynchocephalians, 

 but are pi-obably moi-e neai'ly lelated to the Phytosaurs. I incline 

 to agree with Osborn in placing them in a distinct order, no doubt 

 showing some points of resemblance to the Rhynchocephalians, 

 but not so nearly related to them as is generally held. 



In the following table an attempt is made to indicate the 

 phylogenetic relationships of the Diaptosaurian orders : — 



(COTTLOSAURIAN AnCESTOE) 



(R, P, PI, Permian). 



Pelycosatjeia 

 (F, P, PI, Permian). 



Peouanosaukia 



(Mesosauria) 

 (?, P, Pl, Permian). 

 Pbotoeosauria 

 (P, A, PI, Permian). 



Peocolophonia 

 (R, P, PI, Permian). 



Rhtnchocephalia 

 (F, A, T, ? Triassic). 



Gnathodontia 

 (F, A, PI, Triassic). 



Phytosatjria 

 (F, A, PI, Triassic). 



Peoteeosuchia 



(F, ?, ?, Triassic). 



In the above table the first letter of the formula, R or F, indi- 



