INTRODUCTION. XXXllI 



In noticing the usual habitats of the Diatomacese, I have 

 omitted to mention a locahty not ordinarily accessible — the 

 deeper parts of the ocean — which can only be reached by the 

 dredge of the more enthusiastic and laborious collector. Many 

 interesting species will reward a search conducted with this 

 implement. The magnificent Campylodiscus Horologium, PI. VI. 

 fig. 51, was thus obtained. But these more hidden " treasures 

 of the deep" may be reached in an indirect mode, by employ- 

 ing those fishes or molluscs which frequent deep water, as our 

 substitutes for the dredge. Thus, in the stomachs of the crab 

 or lobster, sole or turbot, the scallop or whelk, such organisms 

 are often found ; and several species, rarely or never occurring 

 in my usual haunts, have been supplied in abundance by a 

 careful dissection of the above microphagists. 



I have also failed to indicate any season as more suitable 

 than another for the researches of the student. I have, how- 

 ever, designedly omitted to do so, as every season is productive 

 of interesting forms. The notes appended to the descriptions 

 of each species, in which I have, when possible, recorded the 

 months in which the species were collected, wiU show how 

 perennial is the supply. Weather permitting, the collector may 

 always reckon upon well-filled bottles, provided his rambles are 

 by the sea-coast, or through a district supplied with ponds 

 and streams. I take my leave of him for the present, by 

 recommending to his pursuit a study pregnant with interest 

 and vn.th beauty ; which fills the mind with wonder in the con- 

 templation of forms at once so minute and perfect, so humble in 

 their individual capacity, and yet by their numbers and wide 

 diffusion occupying an important position in the organic world, 

 and fulfilling the purposes of Power, Wisdom, and Benignity. 



