288 S. L. Penfielcl — Minerals from the 



part of the pectoral limb of Bothriolepis canadensis. The 

 " three elongate narrow hexagons," with "sutures extending 

 from the lateral angles of the hexagons to the border of the 

 spine" described by Cope as characteristic of this spine of 

 Holonema, correspond so exactly to the sutures of the terminal 

 finger of the limb of Bothriolepis canadensis figured by 

 Whiteaves (figures 3 and 4) as to suggest not only generic but 

 specific identity. From the figure given by Cope, with the 

 interpretation of its relations here given, it may be in- 

 ferred that there was some motion at the joint between the 

 two parts of the arm. Pander's dissection and description of 

 the arm of Asterolepis make the movement to have probably 

 been of no great amount. 



It is hoped that other bones or plates may be brought to 

 light illustrating the structure of this interesting genus of 

 fishes. The specimen from which the above restoration was 

 made was found by Prof. C. S. Prosser, near Oxford, ~N. Y. 

 in the Oneonta sandstone, of the lower part of the Upper 

 Devonian. 



Art. XLIY. — On some Minerals from the Manganese Mines 

 of St. Marcel, in Piedmont, Italy ; by S. L. Penfield. 



Alurgite. 



In 1865 Breithaupt gave a brief description* of a deep red 

 mica from St. Marcel, to which he gave the name alurgite, 

 from akovpyos, meaning purple. The portion which he at 

 that time had selected for analysis was accidentally lost and 

 since then it seems never to have been investigated. The 

 writer's attention was called to the mineral by Dr. A. E. Foote 

 of Philadelphia, who sent some of it to New Haven for identi- 

 fication, and a preliminary examination, followed by a chemi- 

 cal analysis and a study of its physical properties have shown 

 that it is a distinct species. Its identity with the alurgite of 

 Breithaupt, was first suggested to the writer by Prof. A. J. 

 Moses of the Columbia School of Mines and has been con- 

 firmed by Prof. A. Weisbach of the Bergakademie at Frei- 

 berg, to whom specimens were sent and to whom the author's 

 thanks are due for comparing them with Breithaupt's original 

 specimens. 



The crystallization of alurgite is monoclinic ; the structure 

 is micaceous and the cleavage basal, though not so perfect as 



*Berg-und Mtteninannisclie Zeitung, xxiv, p. 336, 1865. 



