[lambe] ON NEW SPECIES OF ASPIDERETES 13 



sculpture in these closely allied genera does not afford sufficiently 

 reliable data for a specific determination when the material is 

 fragmentary. 



The above carapace, the type of A spider êtes subquadratus, was 

 found by George F. Sternberg of the vertebrate palaeontological 

 collecting party of 1913. 



In 1902* the writer described an almost complete carapace of a 

 turtle from the Belly River formation on Red Deer river in Alberta, 

 and referred it to Leidy's species Trionyx foveatus from the vicinity 

 of Judith river, Montana, U.S.A. In making this determination 

 the writer was influenced by the sculpture of the proximal half of 

 the costal bone which with other shell fragments, constitute the type 

 material of Leidy's species. It is probable that this Trionyx (Aspi- 

 deretes of Hay) from the Belly River formation of Alberta is distinct 

 from Leidy's species which is not determinable generically. For 

 this turtle, therefore, from the Belly River formation the new specific 

 name maturns is proposed to distinguish it from the form from the 

 vicinity of Judith river, Montana. The name maturus is intended 

 to convey not only the idea of an early appearance in Cretaceous 

 time but also an attainment of general structural characters main- 

 tained by the Trionychidae with little change through later forms 

 to existing species. A s pideretes maturus differs from A. subquadratus 

 principally in the shape of the carapace, the number, form and propor- 

 tions of the neural bones, and the shape and proportionate size of 

 the posterior costals. 



One of the principal distinguishing characters of the Belly River 

 Cretaceous Amphichelydian genus Boremys of the family Baënidœ 

 is the presence in the carapace of supramarginal scutes. In common 

 with other genera of Baënidse imframarginals' occur in the plastron. 



Boremys pulchra'f was described by the writer from material 

 which he collected in 1898 and 1901 in the Belly River formation 

 on Red Deer river, Alberta. In the type specimen the plastron 

 was complete but the hinder half of the carapace was missing. Anoth- 

 er specimen, consisting of the carapace only, supplied valuable informa- 

 tion regarding the number, shape and disposition of the horny scutes 

 but in it most of the sutures between the bones could not be traced. 



*Geol. Survey, Canada, Summary Report for 1901 ; Contributions to Canadian 

 Palaeontology, Vol. Ill (quarto), Part II. 



tContributions to Canadian Palaeontology, Vol. Ill (quarto), Pt. II, p. 43, 

 fig. 8, 1902; Ottawa Naturalist, Vol. XIX, No. 10, January, and No. 12, March, 1906. 



