342 B. S. Lull — Mammals and Horned Dinosaurs. 



than I did some years ago (1912, p. 774) as there seem to be 

 more lines of descent than were recognized at that time. 



Evolutionary sequence. — Lambe (1915)* recognizes three 

 main phyla of Belly River Ceratopsia, two of which lead into the 

 two main groups of Lance forms, the third extending perhaps 

 into the Edmonton but not as yet recognized in the Lance. 

 He dismissed for the present the old Judith River genera 

 Monoclonius and Geratops as being insufficiently characterized. 

 Brown (1914B, p. 550), however, considers Lambe's genus 

 Centrosaurus to be the equivalent of the former. According 

 to Lambe, the separation of these three phyla based upon the 

 main characteristics of the horn-cores and neck frill, appears 

 to be as follows : 



** Eoceratops to f Trieeratops [also \Diceratops\ 

 Large brow-horn increasing in size. 

 Nasal horn persistently small. 

 Squamosal broadly triangular. 

 Parietal fontanelle disappearing (closing). 



** Centrosaurus [= Monoclonius P], **Styraco- 

 saurus, and ** Brachyceratops. \ 

 Brow-horn persistently small. 

 Nasal horn persistently large. 

 Squamosal continuing small. 

 Parietal fontanelle diminishing. 



** Chasmosaurus to f Torosaurus 

 Brow-horn increasing. 

 Nasal horn decreasing. 

 Squamosal lengthening. 

 Parietal fontanelle diminishing. 



In the Lance, therefore, there are two distinct series (Lull 

 1912, p. 774), the Triceratops-Diceratops race and that of 

 Torosaurus. The latter is extremely rare and contains but 

 two species, which may prove identical, as they are very 

 similar and from nearly the same locality, though separated by 

 a stratigraphic interval of about 200 feet. 



Diceratops, with the obsolete nasal horn, represents an aber- 

 rant race of the Trieeratops series, while of the genus 

 Trieeratops itself I can recognize two well-defined phyla and 

 some additional species difficult to place. Of these the first 

 phylum is represented by Trieeratops prorsus, characterized 

 by a well-developed nasal horn pointing forward, and moderate 

 brow-horns. The race includes T prorsus, the closely allied 



*Geol. Surv. Canada, Mus. Bull. 12, p. 15. f Lance. 



X Two genera described by Brown from the Edmonton seem to belong to 

 this group : Anchiceratops, showing affinities with Styracosaurus ; and 

 Leptoceratops, with Brachyceratops. 



** Belly Kiver. 



