Reviews — G. S. Williams's Gabbros of Baltimore. 87 



perfect agreement. This conclusion is open to exactly the same 

 criticism as we offered concerning the ilium. If the only Dinosaurs 

 known were such types as Morosaurus, Atlantosaurus, Brontosaurus, 

 and the allied types described by Professor Marsh, no doubt could 

 exist that the Dinosaurian pelvis was not avian. Nor would its 

 avian resemblances have been sustained by the discovery of such 

 types of animal as have been named Ceratosaiirus, Allosaurus, and 

 Coelurus. Yet it is perfectly true that if Igiianodon, Camptonotus, 

 and Laosaurus, were the only known Dinosaurs, an avian re- 

 semblance might be recognized in the ischiac and pubic bones. 

 But the very fact that these bones vary their forms and change 

 their resemblances within the same order, so as to be avian in some 

 genera, and not avian in others, robs the resemblance of all taxo- 

 nomic importance, and demonstrates that the character of an order 

 or sub-class cannot at the same time be both avian and not avian. 

 The resemblances accordingly sink to the value of sub-ordinal 

 characters, by which some Dinosaurs may be differentiated from 

 others, and are thus proved, I think, to owe their remarkable avian 

 forms to conditions of existence. Exception is taken by M. Dollo to 

 certain details in Mr. Hulke's restoration of the pelvis of Iguanodon, 

 stating that in Iguanodon Mantelli the pubis is not inclined ventrally 

 inward and forward, but, on the contrary, ventrally forward and 

 outward, like the rudiment which exists in birds. There is no 

 symphysis pubis. The post-pubis is not continued to the extremity 

 of the ischium, and is therefore not applied against it in the distal 

 region. M. Dollo also takes exception that the Brussels specimens 

 show by the way in which pi'ocesses from the ischium extend in 

 front of the pubis, two foramina, instead of the one shown in Mr. 

 Hulke's restoration. M. Dollo is certainly correct with regard to the 

 structure in the genus represented by I. Bernissartensis ; but he has 

 presented no evidence that Mr. Hulke was incorrect in his restoration 

 of the pelvis of Iguanodon. He objects to the identification of the 

 pre-pubis of Iguanodon with the small process which is similarly 

 placed in birds, by showing that the supposed pre-pubic structure 

 is developed from the ilium in the common fowl, and cannot there- 

 fore be homologous with the pre-pubis of Iguanodon and other 

 Dinosaurs. The author enters into many details to contest the 

 views which have been advanced by Sir Eichard Owen concerning 

 the interpretation of the pelvis of Dinosaurs, and does good service 

 in bringing under the notice of continental writers the more modern 

 interpretations which, we may say, without any disparagement to 

 M. Dollo's originality, have long been current in this country. 



H. G. Seelet. 

 {To he continued.) 



II.— United States Geological Survey: Bulletin No. 28. The 

 Gabbros and associated Hornblende Eocks occurring in 

 the Neighbourhood of Baltimore, Md. By G. H. Williams. 

 Pp. 59 and iv. Plates. (Washington, 1886.) 



THIS is a valuable contribution to American petrology, and many 

 of the conclusions established must have a special interest for 



