70 TRANSACTIONS OF THE [JAN. 23: 
trisoctahedron 2-2 were observed and determined on a few 
individuals. Instead of the ordinary striations parallel to 
intersections of the cube and pyritohedron, these crystals have 
others on the faces of the octahedron, diploid and pyritohedron 
and parallel to the intersections of these with one another. The 
octahedral faces also show striations parallel to their intersec-. 
tions with the cube. 
The paper was discussed by Messrs. Kunz, Kump, and Braun. 
Dr. Moses next described a mineral from Arizona which 
seemed to be equivalent to the rare sulphate Httringite, hitherto. 
only known in minute crystals at Ettring, Switzerland. 
The Arizona mineral resembles pectolite in appearance, but 
is soft and silky, and occurs in fine, white, radiating fibres upon. 
a silicate of the same bases. The exact composition has not. 
been determined, but approximately it may be given as a basic 
sulphate of lime and alumina. One analysis recalculated after 
deduction of gangue showed CaO., 26.32, ae » 9.85, S05 
18.53, H,O., 45.30. 
The papers are to be published in full in the American 
Journal of Science. 
Mr. L. MclI. Luquer, ‘‘On the Optical Properties of Cacoxen- 
ite from various Localities,’ and ‘‘ The Optical Properties of 
Muscovite from the Kingsbridge Ship Canal.” 
On Trachosteus and Mylostoma, Notes on their: 
Structural Characters. 
BY DR. BASHFORD DEAN. 
ABSTRACT, 
The discovery of the derm plates of the entire anterior- 
portion of the trunk of JZylostoma makes another and important. 
addition to our knowledge of the American Arthrodira, 
The material collected from the Cleveland shale at Linton, 
Ohio, by Rev. William Kepler has recently been added to the 
Museum of Columbia College. In the present specimens the 
crushed plates, as displayed upon the slab of clay ironstone, 
show that the fish was a small one in the group of kindred forms 
from this horizon. It measures from tip of ethmoid to termina- 
tion of dorsal shield about fifteen inches. 
