82 Notices of Memoirs— Prof . 0. C. Marsh- 



Jurassic Dinosaurs is in ascertaining tlie affinities of the dirainntive 

 forms which appear to approach Birds so closely. These forms were 

 not rare, but their remains hitherto found are mostly fragmentary, 

 and can with difficulty be distinguished from those of Birds, which 

 occur in the same beds. Future discoveries will, without doubt, 

 throw much light upon this point. 



Comparatively little is yet known of Cretaceous Dinosaurs, 

 although many have been described from incomplete specimens. All 

 of these appear to have been of large size, but much inferior in this 

 respect to the gigantic forms of the previous period. The remains 

 best preserved show that, before extinction, some members of the 

 group became quite highly specialized. 



Regarding the Dinosaurs as a sub-class of the Eeptilia, the forms 

 best known at present may be classified as follows : — 



Sub-Class DINOSAUPJA. 



Preraaxillary bones separate ; upper and lower temporal arches ; 

 rami of lower jaw united in front by cartilage only ; no teeth on 

 palate. Neural arches of vertebree united to centra by suture ; 

 cervical vertebrae numerous ; sacral vertebi'ge coossified. Cervical 

 ribs united to vertebrse by suture or ankylosis ; thoracic ribs double- 

 headed. Pelvic bones separate from each other, and from sacrum ; 

 ilium prolonged in front of acetabulum ; acetabulum formed in part 

 by pubis ; ischia meet distally on median line. Pore and hind 

 limbs present, the latter ambulatory and larger than those in front ; 

 head of femur at right angles to condyles ; tibia with procnemial 

 crest ; fibula complete. First row of tarsals composed of astragalus 

 and calcaneum only, which together form the upper portion of ankle 

 joint. 



(1.) Order Satjropoda (Lizard foot). Herbivorous. 



Feet plantigrade, ungulate ; five digits in manus and pes; second 

 row of carpals and tarsals unossified. Pubes projecting in front, 

 and united distally by cartilage ; no post-pubis. Precaudal vertebrge 

 hollow. Fore and hind limbs nearly equal ; limb bones solid. 

 Sternal bones pai'ial. Premaxillaries with teeth. 



(1) Family Atlantosauridce. Anterior vertebrae opisthocoelian. 

 Ischia directed downward, with extremities meeting on median line. 



Genera Atlantosaurns, Apatosaurus, Brontosanrus, DijAodocus, 

 ? Camarasavriis (Amphiccelias) , ? DystroplicBus. 



(2) Family Morosauridce. Anterior vertebrae opisthocoelian. 

 Ischia directed backward, with sides meeting on median line. 



Genus Morosaiirits. 



European forms of this order : Bothriospondylus, Cetiosaurus, 

 Chondrosteosaurus, Eucamerotus, Ornithopsis, Pelorosaurus. 



(2.) Order Stegosatjria. (Plated lizard). Herbivorous. 



Feet plantigrade, ungulate ; five digits in manus and pes ; second 

 row of carpals unossified. Pubes projecting free in front ; post- 

 pubis present. Fore limbs very small; locomotion mainly on hind 

 limbs. Vertebr£e and limb bones solid. Osseous dermal armour. 



