394 On the Flint Nodules of the Trimmingham Chalk. 



siliceous casts of Foraminifera, after the following observa- 

 tions by Carter. In a letter, dated June 16, 1875, he writes, 

 " . . . . the dumb-bell form you pointed out to me has almost 

 close to it the original kind of test (silicified) from which it 

 appears to have come, thus : — 



"Correctly drawn to the same scale, viz. -^j- to T -^ z inch. 



" A is the dumb-bell or cast of the chambers (e) of the 

 Organism ; a, the cast of the tube which connected the 

 chambers. 



" B is the silicified foraminifer, b the test, c c the chambers. 

 A little tube seems to have been prolonged from one chamber 

 (d), and may have been connected with another chamber or 

 cast. Thus the dumb-bell is a cast of a couple of chambers 

 of a Foraminifer connected by the intervening tube."] 



In concluding this description of the various kinds of 

 spicules I would add that in the majority of cases I regard 

 the identifications and generic groupings proposed as provi- 

 sional only. It is with many misgivings that I have made 

 many of them ; and nothing but the fact that I had under- 

 taken the task of classification would have induced me to 

 continue what I have felt at times to be a hopeless endeavour. 

 Some kind of order, however, has been evolved out of chaos, 

 though probably not that which wculd result if, by any process 

 of magic, the spicules could be restored to their proper places 

 in the structure of their original owners. 



Many forms of spicules remain undescribed ; those here 

 represented have been derived from two or three small flints 

 only. Of the rich sediments which remain from some twenty or 

 thirty other specimens I have made no use in this paper ; they 

 remain for future observation, and are at the disposal of any one 

 who would care to examine them. 



Mineral Condition of the Spicules. — The spicules are white 

 and opaque when viewed in air by reflected light ; in water 

 or other media they are highly transparent, but without the 



