40 FOSSIL REPTILIA OF THE 



the Pelorosauriis, in the 'Transactions of the Royal Society' for 1850; but, unfortu- 

 nately, the mistake of the anterior for the posterior surface of the bone — viewed as a 

 humerus — in that memoir, vitiates the description, and must have added to the 

 difficulty of comprehending, and to the doubts respecting, the nature of the bone, 

 felt by the anatomists acquainted with it only by the figures and text in the ' Philo- 

 sophical Transactions.' It may be that some transposition and misarticulation of the 

 skeleton of the Gavial, in the museum of the eminent physiologist, whose aid 

 Dr. Mantell acknowledges, occasioned the mistake. According to the analogy 

 of the humerus of the Crocodile, the posterior contour of the shaft of the bone 

 IS concave above, convex below ; but in a less degree in the Pelorosaurus. This 

 longitudinal concavity would, however, be more marked in the specimen had the 

 posterior part of the head (wanting at a, figs. 1 and 3) been preserved, and had 

 the three pieces in which this half of the shaft was extracted from the matrix 

 been a little more naturally joined together. The proximal end of the bone is 

 transversely oblong, moderately convex, with both anterior and posterior borders 

 broken away, but leaving the latter more prominent and convex. The internal angle 

 or tuberosity {%), which, if entire, would have confirmed so satisfactorily the determi- 

 nation adopted, is also broken away. A still larger proportion of the external 

 side of the proximal end is wanting, leaving only the lower end of the deltoidal ridge 

 (fig. 2, d). This, however, reaches three sevenths of the way down the bone, 

 but subsides, and probably begins, nearer the proximal end of the humerus than in 

 the Crocodiles. It projects forward, and bears the same relative position to the 

 fore and outer parts of the bone in Pelorosaurus as in Crocodilia. The transverse 

 concavity on the inner side of the deltoidal process is continued lower down upon the 

 shaft of the bone of the Pelorosaurus, which shaft is more compressed from before 

 backward, giving a longer and narrower sub-elliptical section (Tab. XII, fig. 4) 

 than in the Crocodilia. Below the middle the shaft gradually expands to the distal 

 end, the condyles of which project chiefly from the fore part of the bone, as in 

 the Crocodile : they are, however, more unequally developed, the outer one (figs. 

 2 and 5, c) being much the largest.* There is an indication of a low ridge diverging 

 to the outer and fore part of the outer condyle, as in the Crocodile. 



At the back part of the humerus of the Pelorosaurus, the upper half shows 

 a minor degree of longitudinal concavity, and a lower and more regular transverse 

 convexity, than in the Crocodiles. There is a foramen for the medullary artery 

 at the middle of the back of the shaft, where I have observed it in some Crocodilia 

 (e. g. Croc. Hastingsice). At the lower half the surface, instead of being flat, 

 is transversely concave at the middle, or more concave and with such channel 

 more longitudinally extended, than in Crocodilia. The depth has been increased 



■' This character is rather exaggerated in fig. 2. 



