AND AVES OF NORTH AMERICA. 97 



separated by a concave margin from a larger portion at right angles to the shaft. The 

 latter bears an oblique surface for fixed articulation at its extremity. 



In Megadactylus,* the distal portions of the ischia are united on the median line for a 

 considerable distance, and are styloid in form. This portion is evidently distal, from the 

 lack of articular faces and the divergence and flattening of the other extremities. They 

 also resemble the distal extremities in Compsognathus. In Clepsysaurus, the shaft and di- 

 lated extremity are both preserved. The former resembles that of Megadactylus, the latter 

 that of Hadrosaurus in some degree. If the shaft be posterior, the other extremity is an- 

 terior, and the larger dilatation extending at an angle to the shaft supports, no doubt, the 

 iliac articulation. The trihedral shaft indicates a median line of junction. In Hadrosau- 

 rus no part of the shaft presents a face for contact with that of the other side, while in 

 Laelaps such face is very distinct and elongate. From the above, I suppose that the larger 

 extension of the ischium is superior and bears the iliac articulation, that the concave an- 

 terior outline is that bounding the acetabulum, and that the lower dilatation was in con- 

 tact with but not united to the pubis. Thia is the more probable, since it agrees nearly 

 with the arrangement in Iguanodon, as pointed out by Huxley. t It cannot be denied, how- 

 ever, that the supposed iliac articulation in the ischium in Hadrosaurus, bears a remark- 

 able similarity to the median suture presented by the union of the two supposed ischia on 

 the middle line below and distally, as in the pubes of Struthio. In that case, they would 

 be pubes. In a posterior direction and median approximation it will agree also with the 

 known pelvic elements of an interesting Saurian described by Von Meyer (Palaeonto- 

 graphica) from the Wealden of Germany, the Stenopelix valdensis. No attempt has been 

 made, so far as I am aware, to refer this animal to its place. It appears to me in its ver- 

 tebral and pelvic features to be a small Dinosaur allied to Scelidosaurus Owen. The 

 ischia, however, are remarkably prolonged posteriorly, and find a parallel in Compsog- 

 nathus Wagn. 



Believing them to be ischia, the inferior pelvic arches of Hadrosaurus were light and 

 slender, the ischia parallel and light, and entirely incapable of supporting the weight of 

 the animal, as was done by Megadactylus. The tail was no doubt the great support when 

 the head was elevated. 



* The large pneumatic foramina in the vertebrae of this genus, together with those seen in the sacrum of Laelaps, 

 explain the character of similar vertebras described as os quadratum of Iguanodon by ilautell and Owen, and sacrals 

 of Hadrosaurus by Leidy. I regard the latter as indicative of a new genus allied to the Goniopoda. 



f Opportunity of reviewing this part of my essay having offered, I must point out the confirmatory evidence I 

 have derived from Prof. Huxley's recent explanation of the structure of Hypsilophodon, with regard to my determin- 

 ation of the pubes in Hadrosaurus. He proves conclusively its posterior direction, which view I adopt for Hadrosau- 

 rus, contrary to my former supposition. 



AMERI. PHILOSO. SOC. — VOL. XIV. 25 



