OF THE MARSUPIALIA, EDENTATA, AND SIRENIA. 183 



figure 84). They frequently grow in diverging groups, the plates uniting on the plane 

 of symmetry (see plate 20) and also into parallel growths by the same process. Etching 

 figures show the monoclinic character of the symmetry; they appear on the clinopinacoid 

 as pits formed of negative prism and clinodome and show the position of the vertical 

 axis, elongating along the prism. On the orthopinacoid they also appear as pits elongated 

 in the zone of the ortho-axis and on the base they are elongated in the zone of the clino- 

 axis. Twins of the carlsbad type were observed (text figure 85) , the twin axis being the 

 vertical axis and the composition face the clinopinacoid, the edges of the twin matching 

 along the (100)-(010) edge. 



Double refraction is very weak and pleochroism is hardly noticeable. On edge 

 views the extinction is straight and the axis of symmetry b is always the direction of 

 greater elasticity. On the clinopinacoid or flat view the double refraction is only observ- 

 able with the aid of a quartz wedge and the axis of greater elasticity in this aspect nearly 

 or quite bisects the obtuse angle of a and c. The plane of the optic axes is normal to the 

 plane of symmetry and the orientation of the elasticity axes is a = 6; c A 6 = about 37 

 in the acute angle; b A a =50 in the obtuse angle. No interference figure could be 

 observed, but from the very weak double refraction when looking along a it is probable 

 that this axis is the acute bisectrix, Bx a = a, and hence the optical character is probably 

 negative. 



^-Oxyhemoglobin of Thylacynus cynocephalus. 



Isometric, normal. 



Forms observed: Dodecahedron (100), cube (100). 



Angles: 110 A 110=90; 110 A 101=120 (60); 100 A 010=90. 



Habit dodecahedral, generally very symmetrical isometric dodecahedra; some- 

 times, in case of large crystals, in combination with the cube (text figure 86), the 

 dodecahedron usually predominating; also in very small crystals, almost drops, with the 

 dodecahedral axes appearing as points on the nearly spherical mass, and the crystal 

 looking like a trapezohedron. In profile, the crystals present hexagonal outlines (looking 

 along a trigonal axis) or squares (looking along a tetragonal axis) ; in case of the cube- 

 dodecahedron combination, the profile may be octagonal. Looking along a binary axis 

 the aspect is six-sided, but looks orthorhornbic. These crystals generally formed around 

 the edges of the slides and appeared in immense numbers, but only occasional crystals 

 grow to large size; some of these large ones, however, attained a breadth of 1 mm. They 

 are absolutely isotropic, showing no indication of double refraction in any aspect, even 

 when tested by the quartz wedge, etc. Careful examination with the Zeiss microspectro- 

 scope showed no difference between their spectrum and the spectrum of ordinary oxy- 

 hemoglobin. 



VULPINE PHALANGER OR Cuscus, Trichosurus vulpecula. Plate 21. 



The blood was received in a putrid condition and contained numerous 

 globules resembling fat globules. It was prepared in the usual manner and 

 crystallized readily after the slides were covered. The crystals showed no 

 tendency to dissolve, but remained in perfect condition for days. The 

 negatives were taken 24 hours after the preparations were made. It was not 

 found possible to separate the fat or oil from the blood without sacrificing 

 the small amount of material available, and the fat globules, therefore, show 

 in all of the negatives prepared. The color of the solution was very deep, 

 and the color of the crystals was hard to observe. They appeared to be 

 oxyhemoglobin. 



Oxyhemoglobin of Trichosurus vulpecula. 



Monoclinic: Axial ratio a : b : c =0.9163 : 1 : c; /?=55. 

 Forms observed: Unit prism (110), clinoprism (230), base (001). 



