156 LEWIS, ON DIATOMACE.E. 



guard against sources of error arising from the great varia- 

 tion iu size, outline, and striation, and from the absence of 

 certain and positive indications whereby the sporangial may 

 be detected and classified with its typical variety. The want, 

 however, of several important consulting authorities on this 

 branch in the Academy^s library, together with the not 

 always satisfactory character of the material furnishing the 

 data of this paper, often consisting of muds and mixed gather- 

 ings, must be my excuse for any errors or inadvertencies 

 which may be found in its pages. 



Among those to be described will be introduced one or two 

 doubtful forms, probably sporangial, as Amphiprora pulchra, 

 Bailey, and extraordinary varieties of Surirella ovata and 

 Tricerat'mm alternans, both of which last are figured. 



It is proposed to consider the species to be noticed in the 

 following order : 



1. Neiv species and sporangial forms. 2. Rare species and 

 species not hitherto noted as belonging to this country. 3. 

 Species characteristic of the American coast. 4. Species of 

 universal distribution. 



The precise locality and nature of the gathering from which 

 specimens have been derived will be indicated, excepting 

 where species are of general distribution and very abundant 

 along the coast, along with such other distinctive characters 

 as may be necessary for the definition of new or doubtful 

 species ; and as it is not intended that the summary shall 

 present a complete resume of native marine species, mention 

 of many forms known to me, but not referable to one or other 

 of the above four divisions will be omitted. 



It may not here be out of place to add, that the result of 

 my limited investigations convinces me that a rich and unex- 

 plored field lies open in the United States for those whose 

 time and attention may hereafter be directed to this branch of 

 microscopic research, a branch, until very recently, compara- 

 tively neglected in this country. Perhaps a reason for this 

 neglect may be found in the great interest attaching to the 

 less laborious study of the numerous fossil diatomaceous 

 deposits of our country, and of the new and ever varying 

 guanos so frequently finding their vray to our shores. With- 

 out any intention of undervaluing the importance of researches 

 on fossil botany, it may yet be doubted whether results so 

 satisfactory and important to science are likely to accrue as 

 when the living forms are the subject of study. Nothing 

 certainly would seem so well calculated to damp the ardour 

 of physiological inquiry as prolonged and laborious examina- 

 tions of the minute details of the siliceous skeletons of these 



