PELVIS OF POLICANTHUS. 149 



close general resemblance, especially as regards tlie form of the 

 sacral ribs, and the deep pits by which they are separated from one 

 another; these pits being apparently roofed over by an inward 

 extension of the upper part of the ilium. The same features are 

 noticeable in the apparently generically identical American Dinosaur 

 of which the pelvis and sacrum are figured by Prof. Marsh as 

 Stegosaurus. 



The chief characteristics of the specimen under consideration are 

 shown in the accompanying figures. 



As the result, then, of my study of this specimen, it appears that 

 it indicates a Dinosaur which may be referred to Polaeanthus ; and 

 the question then arises whether or no it is specifically identical 

 with the typical P. Foxil. 



Now, so far as the crushed condition of the pelvis and sacrum of 

 the latter admits of forming a definite opinion, the corresponding 

 portions of the present specimen appear at first sight to be of a 

 decidedly more massive type. It is quite possible, however, that the 

 crushing and maceration which these bones have evidently undergone 

 in Mr. Hulke's specimen may have somewhat exaggerated these 

 apparent points of difference, and that the two ilia are not very 

 different. 



A more important point of distinction remains to be noticed. As 

 is beautifully shown in Mr. Hulke's plate, the upper surface of the 

 dorsal shield of P. Foxii carries a number of bosses for the articula- 

 tion of the large spines found in association with the figured 

 specimen. In Mr. Beckles's specimen, on the contrary, the 

 corresponding surface of the dermal armour is perfectly flat, without 

 the faintest trace of such bosses. It might be urged that the 

 absence of these bosses is due to the effects of rolling on the shore ; 

 but the other parts of the specimen do not show signs of excessive 

 rolling, and it would surely require a great deal of such action to 

 remove all traces of these bosses if they ever existed. 



It appears, however, impossible to be absolutely certain in regard 

 to this point ; but if subsequent ' finds ' should prove that in this 

 Dinosaur the dermal armour was smooth, I would suggest that the 

 species might be appropriately named after its discoverer, Mr. 

 Eeckles. 



It is unfortunate that both extremities of the ilium of this 

 specimen are broken away, so that we cannot determine the relative 

 lengths of its pre- and post-acetabular processes ; but in spite of tliis 

 deficiency the specimen itself is of importance, as showing more 

 clearly than hitherto the close affinity existing between Polaeanthus 

 and the larger Dinosaurs described as Omosaurus and Stegosaurus} 

 The remarkable character of the dermal armour of the latter, as 

 lately restored by Prof. Marsh, amply serves, however, to establish 

 its generic distinctness from Polaeanthus. 



^ [Since this paper was sent in to the Society Prof. Seeley {supra, pp. 81-85) 

 lias more fullj^ described the ilium of Polaeanthus, and indicated the relation- 

 ship of the genus to Stegosaurus and the so-called Omosaurus. I doubt, how- 

 ever, whether he has allowed sufficiently for the effect of crushing. He considers 

 the present specimen (supra, p. 84) as generically distinct from P. Foxii. — Feb. 

 1892.] 



