Jackson.] 82 [November 21, 



These drawings will serve to illustrate the remarks made in refer- 

 ence to the difficulty in the study of diatoms, from the many species 

 named by microscopists, which really ought to be called varieties of 

 species already published. 



The great similarity in the structure of these forms is very notice- 

 able, the blank space in the centre being more or less developed, the 

 striation on each side of the central line, and the striated margin or 

 border broad, as in the type form of N. lyra, or narrow, as in N. prce- 

 texta. 



If the student will examine the published forms of N. lyra, N. 

 speciabilis, N. prcetexta, N. clavata, N. nehulosa and N. Hennedyi, 

 he can not but see the great resemblance there is in structure one to 

 the other. Most of these forms can be found in Prof. W. Gregory's 

 paper on " Marine Diatomaceae, found in the Firth of Clyde and in 

 Loch Fine," published in the transactions of the Royal Society of 

 Edinburgh, 1857, and in his paper on "Glenshira Sands," in the Quart- 

 erly Journal of Microscopical Science, 1854. In this last named pa- 

 per. Prof. Gregory speaks of this same difficulty in knowing just 

 where to place many of the new forms discovered, unless they are 

 called varieties of species already established. 



Mr. Charles G. Bush, to whom I am greatly indebted for assistance 

 in examining this gathering, has found in it some very curious and 

 new sponge spicules. When time will permit, I will give drawings 

 of some of the most remarkable of them. 



November 21, 1866. 



The President in the chair. Forty-seven members present. 



Dr. C. T. Jackson, in referring to his remarks on a meteo- 

 rite at the previous meeting, stated that he had recently re- 

 ceived a paper from Daubree upon the subject. 



In this essay, the author referred to the non-occurrence of any 

 meteorites in any sedimentary strata, attempting to account for it on 

 one of two hypotheses. 1st, that meteoric phenomena may not have 

 taken place when these sediments were at the surface of the earth, 

 and 2d, that the matter then coursing in the heavens, constituted 

 larger unexploded masses with oxydized crusts, so that if they had 

 fallen, they would not be recognized as meteorites. Dr. Jackson, 

 however, believed that too small a superficial area of the sedimentary 



