NATUEAL SCIENCES OF PHILADELPHIA. 239 



regarded (Tab. viii, fig. 6) as the first phalange of the fourth digit, to the me- 

 tatarsal of the same, the phalange referred to the second may find another 

 place. The fifth digit also rests on the evidence of one phalange only. Though 

 the reasoning of Deslongchamps in referring these pieces is good, it seems to me 

 that renewed study might result in ascribing to this genus three toes anteri- 

 orly and one appendicular, — his first. 



The predominance of Reptilian characters in the Dinosauria, as indicated by 

 the structure of the vertebras and other points, renders it probable that the 

 vertebral column did not present that remarkable flexure where the cervical 

 and dorsal series are joined, which is seen in the birds, but rather that they 

 were more or less continuous, and formed a continuum from the sacrum to 

 the nape. The cervicals may have been somewhat elongated, as in some birds, 

 yet this is not probable in view of the necessary balance to be preserved, which 

 would not admit of much projection of the cranium anteriorly. The cervicals 

 of Hadrosaurus are not so long as in the modern Varani ; in Iguanodon they 

 are similar, while their rather oblique articular faces indicate the elevation of 

 that region, and of the position of the cranium. In the case of these animals, 

 there is not the same necessity for a long neck as in the birds, for even in Lae- 

 laps and other genera which probably never used the fore limbs in progression, 

 they furnished a support to the body when the head was employed in taking 

 food, etc., on the ground. 



The caudal region affects the general proportions of a vertebrated animal 

 materially. In Lselaps it is shorter than in any known Dinosaur, measuring less 

 than the hind limb by half a foot. It was cylindrical, slender towards the tip, 

 and in fact not unlike that of a dog, and probably capable of motion similar to 

 the latter. When the Laelaps stood erect, the tail would trail its extremity on 

 the ground, but could furnish little support. 



Comparison with other Dinosauria. 



41 The species with which detailed comparisons can be made, arc the Poecilo- 

 pleurum bucklandii Deslongchamps, and Megalosaurus bucklandii 

 Mantell. All three were of nearly similar size. The Poecilopleurum is better 

 known than the Megalosaurus, and furnishes many similar parts. Thus the 

 humeri possess the same disproportionately small size, the extremity of the tibia 

 is similarly expanded and flattened, and is similarly embraced by the astraga- 

 lus. There are, however, abundant specific differences in all the bones described 

 by Deslongchamps. In the same manner the Laelaps aquil unguis presents 

 abundant specific differences from the Megalosaurus bucklandii. The 

 slender curved femur diff'ers from the massive straight one of the latter ; the 

 tibia is more slender, and more flattened distally ; its extremity is wedge- 

 shaped, not rhombic as in the European species. The claws of Megalosaurus 

 are relatively shorter and less curved. 



The generic relations with these two types must be understood. Laelaps is 

 obviously distinct from Poecilopleurum in the structure of its feet. In the 

 former the phalanges are slender, in the latter massive, and mostly broad. The 

 claws are more diflerent ; in the former compressed and hooked; as broad as 

 deep in the latter, and but little curved. They are prehensile in the former, in 

 the latter not at all, or adapted only for defense ; they present a very small 

 point of insertion, compared with the large knob of the former ; they also ex- 

 hibit a deep groove on the side, which is weak in Lielaps. The difi"erence in 

 this respect is about that between a raptorial and rasorial bird. 



As compared with Megalosaurus, Laelaps probably had very short fore-limbs. 

 I have pointed out the difference in the femur, which is perhaps not more than 

 specific, though this cannot be positively asserted. The difference in the form 

 of the extremity of the tibia I suspect also to indicate more than specific differ- 

 ence. The bone described by Owen (Paheontographical Society) as scapula, 

 furnishes means of estimating the size of the humerus. The glenoid cavity is 



1868.] 



