428 THE MICROSCOPE. 



Plaurosigma Fasciola, fine shell, 86,000 in the inch, cross lines. 

 ,, strong shell, 64,000 in the inch, cross linos. 



Strigosum, 72,000 in the inch, diagonal lines. 



Angulatum, 51,000 in the inch, diagonal lines. 

 Quadratuni, 50,000 in the inch, diagonal lines. 



fcpencerii, 50,000 in the inch, cross lines. 



Attenuatum, 42,000 in the inch, cross lines. 



,, Balticum, 40,000 in the inch, cross lines. 



Formosum, 32,000 in the inch, diagonal lines. 



Strigilis, 30,000 in the inch, cross lines. 



Mr. Norman, of Hull, has favoured us with the follow- 

 ing : 



HINTS FOR COLLECTING DIATOMACEJ3. 



These minute forms are found in all waters, but the 

 most interesting species are those found in salt water, 

 especially shallow lagoons, salt water marshes, estuaries of 

 rivers, pools left by the tide, &c. 



Their presence in any quantity is always shown by the 

 colour they impart to the aquatic plants and sea-weeds 

 they are found attached to, and it' found on the mud, 

 which is very frequently the case, they impart to it also a 

 yellowish brown colour approaching to black brown, if in 

 great numbers. This brownish pellicle, if carefully re- 

 moved with a spoon (without disturbing the mud) will be 

 found very pure. Capital gatherings of Diatomaceae 

 might be obtained by carefully scraping the brown coloured 

 layer from mooring posts, and piles of wharfs and jetties. 



In clear running ditches the plants and stones have 

 often long streamers of yellowish brown slimy matter 

 attached to them, which is generally entirely Diato- 

 maceous. 



When found in large quantities on the mud the layer 

 is often covered with bead-like bubbles of oxygen. This 

 often detaches them from the bottom and buoys them to 

 the surface, where they form a dense brown scum, which 

 is blown to leeward in large quantities, and presents the 

 general appearance of dark-coloured yeast. In this form 

 it may be collected in abundance, often quite free from 

 particles of sand and other impurities. Good and rare 

 species have been obtained from the stomachs of oysters, 

 scallops, and other shell-fish inhabiting deep water. The 

 sea-cucumbers (Holothuridae) found so frequently in 

 southern latitudes contain many species. These animals 



