AND AVES OF NORTH AMERICA. 



121 



This gentleman observing that the gradual advance of the tide, owing to the slow depres- 

 sion of the coast line, was undermining a long bank of the cretaceous clay, carefully 

 examined the debris, from time to time, and made the discovery of the fragment men- 

 tioned. No other portions rewarded his search, and as the bank has been gradually 

 carried away since, there is little probability of the remainder being found. 



The specimen consists of the extremity of the tibia with anchylosed astragalus, with 

 part of the shaft and distal portion of the fibula adherent. From this the character of 

 the genus may be derived, as follows : 



Astragalus confluent with calcaneum, both together anchylosed to the tibia: articular 

 face directed downwards and a little forwards. Fibula slender, articulating with the first 

 tarsal hone. Medullary cavity of tibia small, occupied by a coarse cancellous tissue. 



This genus confirms remarkably the propositions suggested by the remains of Laelaps, 

 as to the probable continuity of the tarsal and tibial elements in certain of this order, and 

 the relation of the fibula to the same. It proves that the latter bone has been reversed in 

 the descriptions of Iguanodon and I ladrosaurus. 



The suture connecting tibia and astragalus is distinct, so that I suspect that the latter 

 is distinct from the; former during a. part at least of the early life of the animal. Thus 

 there is the usual "parallelism" between the adult Orthopod and young Sympbypod. 

 There is an obliquity of the- articular extremity to the axis of the tibia, indicating a 

 prominence of the external tuberosity. 



The fibula is subtrilateral, the posterior face being obtusely angular and fitting a. slight 

 groove, as in I ladrosaurus. The extremity presents an obtuse condyle inwards and down- 

 wards, which is applied to a corresponding concavity of the superior projecting face of the 

 astragalo-calcaneum. The external angle is slightly prominent and angular. 



The affinities of this genus are perhaps in some degree to 1 ladrosaurus ; certainly 

 nearer to it than to Laelaps. The inferior presentation of the ankle joint indicates short 

 metatarsals, so that the form was probably heavy footed. 



ORNITHOTARSUS IMMANIS, Cope. 

 Proceed. Amer. Philos. Boi., 18(ii), p. 117, 



The aooompanying cuts will give a, good idea of the proportions of this fragment. The extremity of the tibia, 

 exhibits the anterior longitudinal concavity common to all the types of the order, and which as in them, is occupied 

 by the ascending apophysis of the astragalus. The astragalo-calcaneum is a thin bone, and does not cover the 



extremity of the tibia internally and posteriorly. It thins out posteriorly and leaves a strong groove to mark the 



suture, apparently for Ligamentous insertion. The transverse plane of the articular face is nearly even ; and it is 

 little contracted medially, much less than in Laelaps aquilunguis. 



As compared with Hadrosaurus foulkii, which it most resembles, the extremity of the tibia presents many 

 differences. First, the external face is much narrower, and more transverse, forming thus a, less open angle with the 

 posterior face. Second ; the anterior concavity is less profound, giving the outline a more transverse direction. 

 AMERi. l'HTLOSO. SOC VOL. XIV. 31 



