Academy of Bcience. 45 



imperfect specimens may be found that can not be generically separated from 

 others in remote formations, and where to unite them would be doing violence to 

 our preconceived opinions of the persistence of geological types. But, on the 

 other hand, the indiscriminate application of names to genera, that can neither be 

 positively united with, or separated from, previous ones, is pernicious. 



The group of saurians represented by these four or five genera, including also 

 Amp/iicoelias and Biplodocus, together with Ceteosanrus, Owen and other European 

 ones, have been characterized by Marsh under the name Sauropoda, which, 

 together with Huxley's Ornithoscelida, or true dinosaurs, have been made subor- 

 ders of Dinosmiria. They are intermediate between the crocodilia and true dino- 

 saurs. Tliey were the largest of terrestial animals, herbivorous, probably amphib- 

 ious, and awkward and slow in their movements. The head, and especially the 

 brain, was very small, the neck long, the dorsal vertebrse massive in their propor- 

 tions, but cavernous and pneumatic, so interlocked as to give great strength and 

 but little breeding. The sacrum of several vertebne, solidly united, and the tail 

 heavy and long. They walked upright upon all four nearly equal massive legs ; 

 the feet with five short toes. The largest of these described by Prof. Marsh could 

 not have been less than eighty feet in length and twenty feet in height, and, prob- 

 ably, thirty tons or more in weight. Although of such almost incredibly gigantic 

 proportions, they were doubtlessly inoffensive and harmle-s in their nature, relying 

 neither upon agility or defensive weapons for protection, but rather upon size alone. 



Stegosaurns was described by Marsh as a separate order, but it is possibly allied 

 to the Sauroscelida, It was a large reptile with a heavy dermal osseous plates or 

 exoskeleton. 



The Ornithoscelida are represented by Nanosaums, Laosaurus, AUosaurus, Creo- 

 saiirus, and a species referred to the Cretaceous genus Dvytosaurus (Laelaps) by 

 Cope, and indicate three well marked families. 



Nanosaurus was the smallest, and together with (Jompmrjnatlms, from the Euro- 

 pean Wealden, to which it is probably allied, the most ornithic of known reptiles. 

 They were animals scarcely larger than a cat, with short thighs, and long, slender 

 legs, the limb bones being extremely hollow and pneumatic, as in most birds. 

 Thej^ doubtlessly walked erect upon the two hind limbs, with very short and weak 

 fore limbs, and were quick and agile in all their habits. 



Laosaurus was a genus of dinosaurs very closely allied, perhaps identical, with 

 Iguditodon and Hypsiloplwdon of the European Jurassic. They were herbivorous 

 animals, which, in the largest known species, measured perhaps ten feet in length, 

 or, when standing erect upon their hind legs, which they must have habitually 

 used, were about five feet hi<gh. The head was of moderate size and the teeth serrated 

 upon the edges; the neck was short, not at all slender; the shoulders small, and 

 the fore legs not more than half as long as the hind ones. The pelvis showed a 

 singular mingling of the bird and rep ile types. The pubes and ischia, if united 

 in symphyses at the ends very feebly so, and probably not at all. The pubes had 

 two rami or branches, the anterior one, the homologue of the lizard or crocodile 

 pubis, a slender spatulate bone, with free ends; the posterior branch or bird pubis, 

 long, slender rod-like bones, extending back parallel to the ischia, in a manner 

 particularly like the struthious birds. The thigh and leg bones were of nearly 

 equal length, rather slender and hollow; the tarsus very similar to that in the bird, 

 the foot slender and three-toed. The tail was probably rather long and compressed 

 from side to side. Other species were smaller, of less than half the size of the 

 larger ones. They were less bird like than the preceding, but more so than the fol- 

 lowing. 



