14 The Ottawa Naturalist. [April 



trunk compact; fore-limbs minute; hind-limbs long and robust; 

 tail nearly half the total length of the animal, tapering, and 

 with only a slight lateral compression. In the skull there is a 

 large antorbital vacuity, preceded by a very small opening in 

 the centre of a depressed area. No triangular alveolar plates on 

 the inner sides of the jaws. A foramen present in the surangular, 

 far back and near its upper border. No presplenial. Teeth 

 trenchant, powerful, 4 premaxillar3% 13 maxillary and 14 

 dentary. First tooth of the maxilla similar in shape and size 

 to those of the prem axilla. Vertebrae slightly amphicoelous, 

 concave on the sides and beneath; 2 cervico-dorsals, 11 dorsals, 

 5 sacrals, and about 34 caudals. Neural spines short throughout 

 the vertebral column. Chevron bones short, beginning with the 

 first caudal. Transverse processes of the caudal vertebrae de- 

 creasing in size to and ending with the 14th vertebra. Anterior 

 zygapophyses of the posterior caudals greatly lengthened. 

 Scapula longer than the fore-limb. Humerus twice the length 

 of the ulna. Two digits, Nos. II and III, to the manus, of which 

 the phalangeal formula is 2 II, 3 III, the terminal phalanges 

 being claw-bones. Metacarpal IV represented by a proximal 

 vestigial bone. Iliuin elongate, plate-like, with a flat upper out- 

 line and rounded ends. Preacetabular part shorter than the 

 hinder portion, of which both are strengthened on the outer 

 surface by a prominent, overhanging flange running horizontally 

 at midheight. Ischium terminating narrowly below. Pubis 

 ending in a horizontally expanded foot, of which the posterior 

 extension is the greater. Femur about the same length as the 

 tibia. Metatarsals II, III and IV elongate, of which III, the 

 longest, is nearly two-thirds the length of the femur. Meta- 

 tarsal I represented distally by a short vestigial bone, and 

 metatarsal V represented in a similar manner proximally. Four 

 clawed digits to the pes, viz.: Nos. I, II, III and IV, of which 

 the phalangeal formula is 2 1, 3 11, 4 III and 5 IV. Ventral 

 ribs composite, sixteen in number, overlapping at the longitudinal 

 mid-line of the body, and bearing distally slender, closely applied 

 sup p lem en t ar ie s . 



Gorgosattrus librains, apart from its dentition, is remarkable 

 for the extreme shortness of the fore-legs and the great length of 

 the hind ones. The long, narrow ilium rises slightly above the 

 short sacral spines, and, in addition to the horizontal flanges, 

 already inentioned, there are two small strengthening buttresses 

 running upward from the centre of the acetabular border. The 

 length of the metatarsals is surprising. The close application of 

 the vestigial distal end of metatarsal I to metatarsal II is in- 

 dicated by a slightly concave surface on the latter bone, which 



