OTARIID.E, PHOCIVJE, MUSTELID^E, PROCYONID^, AND URSID^E. 263 



Pleochroism is strong, especially when the axis a is visible; the colors are: a nearly 

 colorless, pale reddish; b and c nearly equal and deep red, but the color of b distinctly 

 lower than that of c. Double refraction is strong, and on the base the extinction is sym- 

 metrical; on edge views the extinction varies from up to 20 as a maximum, and 

 most of the edge views of the plates give an extinction angle of 7 or 8, measured from 

 the trace of the base (001), or the long dimension of the plate. In convergent light, the 

 basal aspect shows a dusky biaxial cross; or one brush of such a cross, with traces of the 

 other. The orientation of the elasticity axes is c A a =20, b=6, a A 6 = 1 20'. The 

 crystals with the orthodome developed appear to be orthorhombic, owing to straight 

 extinction along the apparent prism; but this is only straight on the aspects in the zone 

 001-101, and the orientation of the elasticity axes appears to be the same in these as in 

 the others. The plane of the optic axes is the clinopinacoid; the binary axis is the axis 

 of mean elasticity. The acute bisectrix of the optic axes is evidently the axis of greatest 

 elasticity, Bx a = a, and the optical character is hence negative. 



TABLE 43. Crystallographic characters of the hemoglobins of the Phocidce, Otariidce, 

 Mustelidce, Procyonidce, and Ursidce. 



