394 Prof. 0. C. Marsh — Classification of Dinosaurs. 



Genera Atlantosaurns, Apatosaurns, Barosaurus, Brontosaurus. 

 Include the largest known land animals. Jurassic, North America. 

 (Figure 4.) 



(2) Family Diplodocida. External nares superior ; no depression 

 for nasal gland; two antorbital openings; large pituitary fossa; 

 dentition weak, and in front of jaws only ; brain inclined backward ; 

 dentary bone narrow in front. Ischia with shaft not expanded dis- 

 tally, directed downward and backward, with sides meeting on median 

 line. Sacrum hollow. Caudal vertebras deeply excavated below ; 

 chevrons with both anterior and posterior branches. 



Genus Diplodocus. Jurassic, North America. 



Fig. 4. — Brontosaurus excelsus, Marsh. 



Jurassic, "^Vyomiug. 



(3) Family Morosauridce. External nares lateral ; large fossa for 

 nasal gland ; small pituitary fossa ; dentary bone massive in front. 

 Shaft of scapula expanded at distal end. Sacral vertebras nearly 

 solid ; ischia slender, with twisted shaft directed backward, and sides 

 meeting on median line. Anterior caudals solid. 



Genera Morosaurus, ? Camarasaurus (Amphiccelias) . Jurassic, 

 North America. 



(4) Family Pleuroccelidce. Dentition weak; teeth resembling 

 those of Diplodocus. Cervical vertebras elongated ; centrum hollow, 

 with large lateral openings ; sacral vertebrae solid, with lateral 

 depressions in centra ; caudal vertebras solid ; anterior caudals with 

 flat articular faces, and transversely compressed neural spines ; 

 middle caudal vertebra? with neural arch on front half of centrum. 

 Ischia with compressed distal ends, meeting on median line. 



Genus Pleuroccelus. ? Jurassic, North America. 



(5) Family Titanosaurida. Fore limbs elongate ; coracoid quadri- 

 lateral. Presacral vertebras opisthoccelian ; first caudal vertebra 

 biconvex ; remaining caudals procoelian ; chevrons open above. 



Genera Titanosaarus and Argyrosaurus. ? Cretaceous, India and 

 Patagonia. 



Teeth of moderate size. Upper end 



(6) Family Cardiodontidce. leetn or moderate size, upper enci 

 of scapula expanded ; humerus elongate ; fore limbs nearly equalling 

 hind limbs in length. Sacrum solid ; ischia with wide distal ends 

 meeting on median line. Caudal vertebras biconcave. 



