MY/CTEBOSTJCHUS. 135 



Femur : short diameter of middle of shaft 4*0 



width of condyles (approx.) 5-3 



Tibia: length 19-7 



width of upper end 5'7 



,, lower end 4"S 



Front metatarsal : length 12-0 



R. 3898. Left ilium, ischium, and femur of a very large individual, probably of this species. 

 The dimensions (in centimetres) of these bones are : — 



Ilium : length of dorsal border 19 - 



height from acetabular to dorsal border 12"5 



length from anteroinferior to postero-superior angle . 22-9 



Ischium : length of symphysial border .... (approx.) 25'5 



width from acetabular surface to posterior angle . . 23-5 



width of neck 6"8 



greatest width of the proximal end 12*0 



Femur : length in a straight line 53'0 



greatest width of proximal end 9 - 5 



long diameter of middle of shaft 5 - 9 



short diameter of middle of shaft . . . (approx.) 4-0 



This is the largest Steneosaur recorded from this horizon. 



Genus MYCTEH08UCHUS, nov. 



Large Mesosuchian Crocodiles in which the snout is greatly elongated and sharply 

 marked off from the cranial region of the skull, which narrows very rapidly immediately 

 in front of the orbits. The alveolar borders are straight and the teeth slender, 

 though not excessively so ; they were probably not directed outwards as in Teleo- 

 saurus. The temporal fossas are relatively smaller and especially shorter than in the 

 typical Steneosaurs. The upper surface of the skull exhibits a strong rugose sculpture, 

 especially on the frontals. In the mandible the symphysis is long, but is less than 

 two-thirds of the total length. The fore limb is less reduced than in Steneosaurus, and 

 in the humerus both distal condyles are well developed. The tail is very long and the 

 caudal centra are strongly compressed laterally : their neural spines are broad and high, 

 and in the middle and posterior regions deeply notched both anteriorly and posteriorly. 

 The dorsal armour was heavy, the scutes being much more massive than in Steneosaurus. 



This genus has been established for the reception of the only known species, 

 Mycterosuchus nasutus, from the Oxford Clay of Peterborough, a form which differs 

 considerably from any of the species of Steneosaurus, and in the sudden narrowing of 

 the snout has some similarity with Teleosaurus, from which, however, it is distinguished 

 by (1) the straight alveolar borders with downwardly directed teeth, (2) the relatively 

 larger size of the superior temporal fossa?, and (3) the relatively larger head. 



