MORRISON MAMMALS: MULTITUBERCULATA 15 



the same size and each with two rows of cusps, with not over four cusps in any one row. 

 Molar cusps not definitely crested or truly crescentic. 



Type. — Plaglaulax Falconer. 



Distribution. — Purbeckian (upper Jurassic) and Wealden (lower Cretaceous) 

 of England, Morrison (upper Jurassic) of Wyoming. 



In this family the genera Plagiaulax, Bolodon, Cteuacodon, Psalodon, and 

 Loxaidax are now recognized. All but Psalodon occur in England, only Ctemcodon 

 and Psalodon in America. Loxanlax is a Wealden form; the others are from the Eng- 

 lish Purbeck or American Morrison. Bolodon is based on upper jaws, of which three 

 species are known in the Purbeckian, and it probably is synonymous with or includes 

 species of Plagiaulax and (or) Cteuacodon, but it must be retained provisionally until 

 its association with lower jaws shall have been demonstrated. Plagiaulax is known, as 

 such, only from lower jaws. The type of Psalodon is an upper jaw, but a lower jaw is 

 referred. The t)-pe of Cteuacodon is a lower jaw, but an upper jaw is referred. 



The following table gives in resume the present disposition of the American mem- 

 bers of the family: 



Marsh 1887 Present Memoir 



Cteuacodon serratus\ Cteuacodon serrattis Marsh 



Cteuacodon nanus J 



Cteuacodon scindeus Simpson 



Allodou laticefs Cteuacodon laticefs (Marsh) 



Cteuacodon fotens Psalodon fotens (Marsh) 



Allodou fortis Psalodon fortis ( Marsh) 



"^Psalodon marshi Simpson 



Owing to the lack of association of the various parts of the dentition, this list 

 includes several possible synonyms. Psalodon and Cteuacodon are surely distinct, but 

 Ct. laticefs may be the upper dentition of Ct. serratns, and Ps. fortis, Ps. fotens, and 

 Ps. marshi may be respectively the anterior upper, posterior upper, and lower teeth of 

 the same species. If these possibilities should materialize, the list would be reduced to 

 Cteuacodon serratus, Cteuacodon scindeus, and Psalodon fotens. 



Cteuacodon Marsh 1879 



1879. Cteuacodon, Marsh, Amer. Jour. Set. (3) XVIII, 396. 

 1881. Allodou, Marsh, Amer. four. Set. (3) XXI, 511. 

 1884. Pliofrion, Cope, Am. Nat., XVIII, 691. 



Definition. — Four lower premolars. Pa shearing, with or without serrations, 

 relatively larger than in Plagiaulax. Ridges on shearing teeth confined to part near 

 edge. Jaw longer and more slender than in Plagiaulax. P' with three subequal cusps. 

 P* broad, with three outer and four inner cusps, P^ similar but with two outer cusps. 

 Outer cusps well developed. 



Type. — Ct. serratus Marsh. 



Distribution. — Purbeckian, England; Morrison, Wyoming. 



