Prof. 0. C. 3farsh — Families of Sauropodous Dinosauria. 157 



7. In addition to the inferences stated under 6, it is obvious that 

 extensive basaltic eruptions in certain portions of the North Atlantic 

 depression have interfered with the regularity of the suboceanic 

 continental slope. These are associated with terrigenous rocks on 

 the continental side of the slope, but appai'ently not so on the 

 oceanic side. Of the former ease Franz Josef Land and the Hebrides 

 supply noteworthy instances. 



8. With respect to the amount of elevation undergone at various 

 periods along the eastern margin of the North Atlantic basin, there 

 are no very certain data. Speculation on this point should be 

 confined within reasonable limits, and we ought to be content with 

 the minimum divergence from present - day conditions which is 

 required to account for the most obvious facts. Subsequent to the 

 commencement of the Tertiary period, local changes to the extent of 

 500 fathoms would still leave the great depths unaffected, whilst 

 there is no i-eason to believe that any changes to this extent have 

 occurred in Pleistocene times. In Fig. 1 it will be seen that special 

 prominence has been given to the 500-fathom line. 



II. — On the Families of Sauropodous Dinosauria.^ 

 By Professor 0. C. Marsh, Ph.D., LL.D. 



THE subclass Dinosauria, as known to-day, I have divided into 

 thi'ee orders : the Theropoda, or carnivorous forms ; the Sauro- 

 poda, or herbivorous quadrupedal forms ; and the Predentata, also 

 , herbivorous, and including several suborders, namely, the Stegosauria 

 and Ceratopsia, both quadrupedal, and the Ornithopoda, containing 

 bipedal bird-like reptiles.^ 



The principal characters of the order Sauropoda, here discussed, 

 may be briefly stated as follows : — 



Order SAUROPODA. 

 External nares at top of skull ; premaxillary bones with teeth ; 

 crowns of teeth rugose, and more or less spoon-shaped; large 

 antorbital openings ; no pineal foramen ; alisphenoid bones ; brain- 

 case ossified; no columellse ; postoccipital iDones ; no predentary 

 bone ; dentary without coronoid process. Cervical ribs co-ossified 

 with vertebrse; anterior vertebrae opisthocoelian, with neural spines 

 bifid ; posterior trunk vertebrse united by diplosphenal articulation ; 

 pi'esacral vertebra hollow ; each sacral vertebra supports its own 

 sacral rib, or transverse process ; no diapophyses on sacral vertebrge ; 

 neural canal much expanded in sacrum ; first caudal vertebra bi- 

 convex ; anterior caudals procoelian. Sternal bones parial ; sternal 

 I'ibs ossified. Ilium expanded in front of acetabulum ; pubes pro- 

 jecting in front, and united distally by cartilage ; no post-pubis. 

 Limb bones solid; fore and hind limbs nearly equal; metacarpals 

 longer than metatarsals; femur longer than tibia; astragalus and 

 calcaneum not fitted to end of tibia ; feet plantigrade, ungulate ; five 



^ Abstract of communication made to Section D, British Association for the 

 Advancement of Science, Bristol Meeting, September 12, 1898. 



^ The Dinosaurs of North America, Sixteenth Annual Report, U.S. Geological 

 Survey. 84 plates. "Washington, 1896. 



