6 ANNALS NEW YORK ACADEMY OF SCIENCES 



oblique than the type specimens of M . cuneiformis, though some of them 

 have the lobe scarcely more apparent. I am regarding part of these small 

 specimens as being young examples of M. Wyoming ensis, and this may 

 also be the true relationship of the Ouray specimens referred to cunei- 

 formis. Typical cuneiformis should probably be kept distinct for the 

 time being. 



Horizon and locality: Lykins formation; Heygood Canyon (lots 

 3264, 3265 and 3266), Stout (lot 3262) and Perry Park (lot 3263), 



Colorado. 



Myalina perattenuata Meek and Hayden 



The Myalinas of the Lykins formation in addition to showing varia- 

 tion in the amplitude of the posterior wing vary conspicuously in the 

 development of the anterior lobe. Some specimens have scarcely any 

 perceptible development of this feature. These, although they are not 

 sharply distinguished from the typical M. Wyoming ensis, I am separat- 

 ing as a different species under the title M. perattenuata. A similar phe- 

 nomenon was observed in the Myalinas of the Eico formation of the San 

 Juan region, and a similar course was pursued in regard to them. These 

 Lykins specimens, however, are for the most part much smaller than 

 those from the Eico formation and in this character approximate M. 

 cuneiformis, but most of them are distinctly less oblique. A not very 

 considerable breakage along the hinge line of these small shells however, 

 or a concealment of the true outline in that region, makes an appreciable 

 difference in their apparent obliquity. 



Horizon and locality: Lykins formation; Heygood Canyon (lots 



3264, 3265 and 3266), Stout (lot 3262) and Perry Park (lot 3263), 



Colorado. 



Pleurophorus sp. 



A very imperfect internal mold showing best the impression of the 

 hinge structures in the umbonal region, where they possess the charac- 

 teristic dental arrangement of Pleurophorus. For the rest, there is indi- 

 cated a transverse, oblong shell of medium size with rather strongly 

 projecting anterior end. 



Horizon and locality: Lykins formation; Perry Park, Colorado 

 (lot 3263). 



Murchisonia buttersi sp. nov. 



Shell of medium size, slender, with high, many-whorled spire. Length of the 

 type specimen as restored about 25 mm. Diameter of final whorl 11 mm. 

 Number of volutions 10. Volutions angular with a thick, prominent carina 

 situated considerably below the middle, the height of the upper zone being to 

 that of the lower about as 2 to 1. Upper and lower zones more or less planate 



