Shimer and Blodgett — Mt. Taylor Region, New Mexico. 67 



Locality and position, — Two specimens of this species were 

 found in a brownish yellow sandstone at locality A, twelve 

 miles southeast of Cabezon. The strata are of uppermost Fort 

 Benton age or possibly Niobrara. A fragment of another 

 specimen was found at locality B in a brown sandstone of 

 upper Fort Benton age. 



Scaphites sp. 



Several external molds, with a narrow but deep umbilicus 

 and radiating ribs increasing by implantation are referred to 

 this genus. One looks very much like 8. ventricosum. 



Locality and position, — Found in a dark calcareous shale, 

 one mile southwest of Casa Salazar, at Neck 14 ; they were 

 associated with fossils of Fort Benton age. 



Summary. 



The specimens are, as a rule, comparatively well preserved 

 considering that they usually occur on arenaceous beds. The 

 character of the beds likewise explains the predominance of 

 pelecypods over other classes. Moreover the presence in sev- 

 eral of the beds of an abundance of plant fragments indicates 

 also the comparative nearness of land areas. 



As suggestive of an unfavorable environment, it is interest- 

 ing to note the presence of several dwarf varieties of mollusks 

 in various localities in New Mexico, as well as at times extend- 

 ing north into Colorado. Lima utahensis Stanton attained 

 here only about one half the size to which it grew at the type 

 locality " southeast of Paria, Utah," and in the upper Kanab 

 valley, Utah. Ostrea anomioides var. nanus Johnson is a dwarf 

 form of the species O. anomioides Meek. Lueina subundata 

 H. and M. occurs in the Rio Puerco valley slightly smaller than 

 in Utah. The type of Ostrea lugubris Conrad was obtained 

 from the old Santa Fe trail east of Canadian river, New Mexico ; 

 it is spoken of by Stanton as a dwarfed form which, under fav- 

 orable conditions, grows much larger into the forms 0. blackii 

 and 0. bellaplicata. This small form* of O. lugubris is some- 

 what common also in the Mt. Taylor region of New Mexico. 



Massachusetts Institute of Technology 3 

 Geological Department. 



