CHALK MAKERS, OR FORAMINIFERA, 45 



placed very near the bottom in the graduated scale 



of animal life, 



" How each fulfill'd 



The utmost purpose of its span of being, 

 And did its duty in its narrow circle, 

 As surely as the sun, in his career, 

 Accomplishes the glorious end of his." 



It would be almost hopeless to attempt any verbal 

 description of all the various forms of shells which 

 are constructed by the different species of Forami- 

 nifera.. Within certain limits, and in this- instance 

 very broad ones, each species has its own type of 

 shell. This was more true in the days when the form 

 of the shell was the principal character than it is at 

 present, but there are some broad general features 

 which find acceptance now. Primarily, there are 

 three distinct varieties of texture the porcellanous, 

 resembling porcelain ; the hyaline or vitreous, which 

 are more glassy ; and the arenaceous, or sandy. In 

 the first the texture bears a strong resemblance to 

 porcelain, especially when the surface is highly 

 polished. Some of these are ribbed, others are 

 channelled, whilst others are pitted either with small 

 depressions or large areolae. The vitreous shells 

 have almost a glassy transparency, sometimes opaline, 

 and these, again, may be sculptured on the surface 

 with ridges or tubercles. Dead shells, when subject 

 to long action of sea-water, lose their lustre and be- 

 come opaque. Finally, the arenaceous are shells 



