A New Mifieralog-ical Nomenclature. 11 



a 



tire occurring form, the peculiarity of its cleavage, or some 

 peculiar physical or chemical character. In specifying the 

 crystalline form, the following terms have been employed, viz : 

 cubicus, when the primary is a cube ; octahedrus, when the re- 

 gular octahedron ; dodecahedrus, when the rhombic dodecahe- 

 dron ; rhombohedrus, when the rhombohedron ; pyramidalis, 

 when an octahedron not regular ; prismaticus, when a prism, 

 or more particularly a rhombic or rectangular prism. The 

 several right prisms have been designated by a term indicating 

 the base of the prism ; thus quadratics, for right square prism ; 

 rectangulus, rhombicus, rhomboideus, respectively, for right rec- 

 tangular, rhombic or rhomboidal prisms. The term oblxquus 

 has been restricted to the oblique rhombic prism, the oblique 

 rhomboidal being expressed by the adjective Iriclinatus, in allu- 

 sion to the three oblique inclinations of its axes. 



Other more general terms have been occasionally employed, 

 depending on the following classification of the primary forms, 

 founded on the relations of their axes : 



Class 1. Monomelrica, (fxovoc; one, and fJt-Sffov measure) : includes 

 the cube, regular octahedron and rhombic dodecahedron, in which 

 the three axes arc equal, or of one kind. 



Class 2. Dimclricu, (Si$ two, and fj.srgov) : includes the right 

 square prism and square octahedron, in each of which the axes are 



of two kinds. 



Class 3. Trimctrica, (rps three, and f*smv) : includes the right 

 rectangular and rhombic prisms, and the right rectangular and rhom- 

 bic octahedrons, in which the three rectangular axes arc; unequal. 



Class 4. Monodiuala, (fJDovqg one, and xXivw to incline) : includes 

 the right rhomboidal and oblique rhombic prisms in which one of the 

 ihrce axes is obliquely inclined to one of the remaining two. 



Class 5. Triclinaia, (rgis three, and xXivw) : includes the oblique 

 rhomboidal prism, in which all three axes intersect at oblique angles. 



Class 6. Tetraxona, (rsrraga four, and "ccgwv axis) : includes 

 the hexagonal prism and rhombohedron, which have four axes. 



The relations of the forms, in any one of these classes, is such 

 that it may be impossible in some instances, from an entire indis- 



