AKD ON THE EVOLUTION OF THE CKOCODILIA. 427 



vated. The ischia are not greatly prolonged backwards"; and the 

 pubes are directed forwards and inwards. 



The femur has no prominent inner trochanter ; the astragalus is 

 not a depressed concavo-convex bone with an ascending process. 

 There are, at fewest, two longitudinal rows of dermal scutes, one on 

 each side of the middle line of the dorsal region of the body. 



Stagonolepis and Belodon come within the order Crocodilia, as 

 thus defined, and constitute the first of three suborders, which may 

 be distinguished on purely anatomical grounds. 



Suborder I. Pabastichia. 



Neither the palatine nor the pterygoid bones are produced into 

 osseous plates which prolong the nasal passage and give rise to 

 secondary posterior nares. Consequently the nasal chambers com- 

 municate with the mouth by apertures situated beneath the anterior 

 part of the skull. The Eustachian passages are not enclosed by bone. 

 The centra of the vertebras are amphicoelous. The atlas and axis are 

 unknown. The coracoid is short and rounded. The ala of the ilium 

 is high, and has a large and prominent anterior dorsal angle. 

 The acetabular margin is entire, and its centre projects beyond its 

 anterior and posterior ends. The ischium is short dorso-ventrally, 

 elongated longitudinally, and in its acetabular portion resembles 

 that of a Lizard. The characters of the manus and pes are unknown. 



There are two longitudinal series of articulated, carinated, dorsal 

 scutes ; and in Stagonolepis (but apparently not in Belodon) there is 

 a ventral thoraco-abdominal shield, formed of not more than eight 

 longitudinal series of articulated scutes, each of which consists of 

 only one piece of bone. 



Genera. Stagonolepis, Belodon. 



Suborder II. 3JJEsosrcHiA. 



The palatine bones are produced into osseous plates, which prolong 

 the nasal passages and give rise to secondary posterior nares, 

 which are situated beneath the middle of the skull. The pterygoid 

 bones take no share in the formation of the secondary posterior 

 nares. 



A middle Eustachian canal is included between the basioccipital 

 and the basisphenoid, but the lateral Eustachian canals of existing 

 Crocodilia are represented only by grooves*. 



The centra of the vertebras are amphicoelous. The coracoid is 

 elongated, as in the next suborder. The ala of the ilium is less high 

 than in the foregoing, higher than in the following suborder. Its 

 antero-dorsal angle is at most only slightly prolonged. The ace- 

 tabular margin is nearly straight, and hardly, if at all, notched. 



* M. Eudes Deslongchamps was the discoverer of this and many other im- 

 portant characters of the skull, and, indeed, of the general structure of the 

 Mesosuehia. See the classical " Prodrome des Teleosauriens du Calvados," con- 

 tained in the 'ISotes Paleontologiques,' published by M. Eugene Eudes Des- 

 longchamps in 1869. 



