10 PROCJCEDINGS OF THE ACADEMY OF [1884. 



Visual Organa of Lamellibranchs. — Dr. Benjamin Sharp re- 

 ported on his work on the lamellibranch eye. He had examined 

 the edge of the mantle of Ostrea virginica and Mitilis edulis of 

 the Asiphonata, and the siphons of Venus mercenaria^ Mya 

 arenaria, Mactra solidissima, besides the forms already described 

 for Solen ensis and S. vagina (Proc. of Academy of Nat. Sciences 

 of Phila., 1883, pp. 248-9). The pigmented cells found in these 

 parts are essentially the same as those found in Solen ensis and S. 

 vagina. The smallest of all the cells were found in Ostrea and 

 the largest in Venus. Experiments on these forms show their 

 sensitiveness to light and shadow, and the cells showing the 

 retinal character described leaves little doubt as to the power 

 of vision. No nerves could be demonstrated passing direct to 

 these cells, and probably those distributed to the general 

 epidermis serve in transmitting the impressions. The visual 

 IDOwer is so low that nerves have not been yet specialized for 

 this purpose. 



January 15. 

 The President, Dr. Leidy, in the chair. 

 Twenty persons present. 



A Fhosphorescent Variety of Limestone. — Professor Lewis gave 

 a description of a remarkable substance found in one of the 

 mountain mines of Utah, near Salt Lake City, sent to him some 

 months ago by Professor Cope. It is a white rock which phos- 

 phoresces with a lurid red light whenever struck or scratched 

 with a hard substance, and on that account has been called by 

 the miners. Hell-fire rock. 



It proves upon examination to be an almost perfectly pure car- 

 bonate of lime, containing occasionally slight impurities of iron, 

 etc. It is a loose grained, white, crystalline limestone, the grains 

 of which are but slightly coherent, giving the rock the appear- 

 ance of a soft sandstone. Upon slight abrasion in the hand, it 

 crumbles to form a coarse, calcareous sand. Under the micro- 

 scope the rock appears as a loose mass of irregular, angular 

 grains, which are nearly transparent, and which have a lustre 

 resembling that of alum. Portions of the rock are colored slightly 

 yellow by oxide of iron. 



Its phosphorescent properties are very remarkable, entitling it 

 to rank as anew variety of limestone. It was long ago noticed 

 by Becquerel that some limestones were slightly phosphorescent 

 after heating or insolation, but so far as known, no other lime- 

 stone possesses this property in a degree at all approaching that 



