74 
the species of hadrosaurian dinosaurs from the Lance formation as well 
as from the Judith River. This is partly due to the fact that some of the 
early palaeontologists believed the Judith River and the Lance formations 
to be of the same age, and partly because of the difficulty of distinguishing 
genera by the teeth alone. 
In 1902 J. B. Hatcher published an article 1 entitled “The Genera 
and Species of the Trachodontidae (Hadrosauridae, Claosauridae) 
Marsh”, in which he says 
"A careful examination of the original descriptions and figures of the types of the ten 
genera and twenty species (of the Hadrosauridae) enumerated above, shows that there' 
should be a great reduction in each and that the ten genera which have been proposed, 
should be reduced to two, Trachodon Leidy and Claosaurus Marsh, while the remaining 
eight genera should be treated as synonyms of Trachodon which should also be made to 
include T. ( Claosaurus ) annectens Marsh: while the smaller Claosaurus agilis described by 
Marsh from the Kansas chalk may still be considered as pertaining to a distinct genus/' 
That Hatcher was correct in referring annectens to a genus other than 
Claosaurus is evident when it is compared with Marsh's Claosaurus agilis 
and this conclusion has been generally accepted by later writers. That, 
he was correct in assigning all the other species to Trachodon is not so 
apparent. 
It is pointed out by Gilmore 2 and Lambe 3 that the type material 
on which the genus and species T. annectens are based is inadequate, and 
that it is not possible to identify with it better and subsequently discovered 
specimens. Hatcher 4 , at a later date, in discussing the Hadrosauridae , 
says, “It is scarcely possible to identify the various species of this genus 
or the genera of the family from the teeth alone.” 
In more recent years Lambe, Brown, Parks, and Gilmore have; 
described no less than nine genera and fifteen species of hadrosaurian. 
dinosaurs from the Belly River and Edmonton formations of Alberta,, 
based on adequate material, but in no case has a single genus been described, 
from both of these formations, which are closer in time than the Judith 
River and Lance. Among the hadrosaurian caudal vertebrae, from the 
Belly River formation, in the collections of the Geological Survey at. 
Ottawa, there is not one in which the anterior face of the centrum is 
convex; a character common to certain Lance forms. In six years collecting 
from the Belly River formation the writer has not seen a single specimen 
of hadrosaur that could be referred to any of the Lance species. These 
facts, coupled with the differences found in the teeth of Trachodon mirabilis. 
as contrasted with those of the species found in more recent formations, 
seem to be ample reasons, as suggested by Gilmore® and Lambe®, for 
restricting the use of the name Trachodon to a Judith River species. 
The first species, and the only genus of a hadrosaurian dinosaur to be 
described from the Lance formation, was Thespesius occidentalism founded 
by Leidy, in December, 1856, upon two caudal vertebrae and a proximal 
phalanx of the hind foot. 
1 Ann. Carnegie Mus., vol. I, pp. 377-386 (1902), 
* Sci., New Ser., vol. XLI, pp. 668-660 (1916). 
1 Ottawa Nat., vol. XXXI, pp. 136-139 (Feb., 1918). 
* U.S. Geol. Surv., Bull. No. 267, p. 97 (1915). 
* Loc. cit. 
* Proc. Acad. Nat. Sci., Phil., vol. VIII, pp. 303-304. 
