1895 



THE MICROSCOPE. 



53 



shell. Or is your shell spongy, the surface a mass of 

 confused meshes instead of regular pores ? Fam. Spon- 

 gurida. Here again the only note necessary is that a 

 latticed medullary shell is an inner shell with pores. If 

 your shell belongs to div. B, or div. C, you will find no 

 difficulty with the genera. 



But instead of being a true sphere or an elongated 

 sphere, your form may be a disk more or less flattened. 

 Focus on it carefully and see which figure it more resem- 



bles, No. 14, or 16. That is, if it were tilted would it 

 show such protuberances as those in fig. 14 or lack them 

 like fig. 16.^ If the form is a phacoid shell, resembles 

 in shape a bi-convex lens with broad edges, it belongs to 

 div. A. of discoidal shells, in which there are two fam- 

 ilies, the Phacosdiscida and the Coccodiscida. If the 

 margin of the phacoid shell is simple, or only armed 

 with radial spines, it is one of the former, and the num- 

 ber of the spines, and of the inner shells, and the presence 

 or absence of a girdle will give the genus. By this 



