0. C. Marsh — Dinosaurs of N. America. 43 



feature of interest must not be omitted ; it is that the teeth have 

 two distinct roots : this is true both of the upper and lower series. 

 The roots are placed transversely in the jaw, and there is a separate 

 cavity, more or less distinct, for each of them. No fewer than ten 

 vertebrae are co-ossified in the sacrum of Triceratops ; whilst the 

 middle, or true sacral vertebree, have double transverse processes 

 to support the ilium — a character hitherto only seen in Ceratosaurus 

 and other Theropoda. 



Another American type of dinosaur is I'epresented by the genus 

 Claosaurus, from the Cretaceous of Kansas. 



The skull is long and narrow, with the facial portion especially 

 produced, and slightly expanded in front, very like the head of 

 an anserine bird when seen from above. The extremities of the 

 ])remaxillaries are beak-like, and the predentary lione is robust and 

 fitted to meet the strong beak above. The teeth in Claosaurus are 

 confined entirely to the maxillary and dentary bones. They are 

 very numerous, and are arranged in vertical series, so that they 

 succeed each other as the functional teeth are worn away. The 

 number of teeth, as shown in the drawing, may be as many as 38 to 

 40, above and below, on each side, if they are correctly shown 

 on pi. Ixxii, fig. 1 ; but " six or more " is the number mentioned in 

 the text on p. 221 (this should probably be 66). 



The whole vertebral coiuuin was found in position, except the 

 terminal caudals, which are represented in outline. The first and 

 second caudals have no chevrons. Behind these the chevron-bones 

 are very long, indicating a powerful, compressed tail, well adapted 

 for swimming. 



Between the ribs and the neural spines, in the median dorsal 

 region, are very numerous rod-like ossified tendons, which increase 

 in number in the sacral region and along the base of the tail, and 

 then gradually diminish in number and size, ending at about the 

 Soth caudal. These tendons resemble those in the Bernissart 

 Iguauodon described by Dollo, and must have added greatly to 

 the strength of the dorsal region in these old vegetable-feeding 

 dinosaurs, whether in raising themselves into an erect position, 

 or to assist them in the act of running, or swimming, to escape 

 from their carnivorous enemies. 



The tore-limbs of Claosaurus are unusually small in comparison 

 with the posterior. The manus was very long, and had three 

 functional digits : two (2nd and 3rd) were of equal length, but the 

 1st was rudimentary, the 4th was shorter and less developed, and 

 the 5th was entirely wanting. The ends of these phalanges were 

 blunt, and were probably covered with hoofs and not with claws. 

 The hind-foot, or pes, had but three digits (as in Iguanodon), and 

 the terminal phalanges were covered with bi'oad hoofs. 



In the conclusion comparisons are made, by means of a series 

 of figures, of the various parts of dinosaurs. Skulls are depicted 

 of typical genera of such herbivorous forms as Triceratops, Clao- 

 saurus, Camptosaurus, and Diplodocus, giving the brain-cavity in 

 position, to illustrate the diminutive size of the brain in each in 



