460 PROCEEDINGS OF THE ACADEMY OF [May, 



A NEW DIATOM. 

 BY T. CHALKLEY PALMER. 



Iii April and May of 1905, and at about the same season in later 

 years, gatherings from swampy pools near Media, Pa., often showed 

 little groups of freely motile naviculoid diatoms. These groups at- 

 tracted notice from the curious circumstance that they seemed always 

 composed of four individuals. Also, they were essentially unlike 

 any filamentous forms such asEunotia and Melosiru, and differ equally 

 with the short blocks of Gomphonema, Stauroneis. etc., which may 

 temporarily remain in contact after reduplication. All of these, and 

 with them the chains or bands of infinitesimal Naviculae of the group 

 Diadesmis, are alike in that the contact between adjacent frustules 

 is by the joining of valve to valve. But these were joined girdle to 

 girdle, so that the group as a whole moved about with four parallel 

 raphes in approximate contact with the substratum, while four other 

 parallel raphes were in evidence on the top. Staining with Bismarck 

 brown and tannin showed each group to be enclosed in a mass of 

 coleoderm. This coleoderm, of varying consistency, sometimes 

 coagulates in place under the treatment, and sometimes, being more 

 fluid and expanded, collapses confusedly as a brownish cloud upon the 

 supporting slide (Plate XXXV, fig. 1). 



These groups were at first supposed to constitute merely a temporary 

 condition of some well-known species, and search was made for the 

 same diatom in the isolated state normal to the Xaviculse, especially 

 to the species of the Pinnularia 1 division of the genus, to which the form 

 obviously belongs. But the groups have continued to occur while the 

 isolated diatom has been nowhere visible. Moreover, a closer study 

 of the frustule has indicated a new and curious species. 



In May, 1909, rich gatherings were made of this diatom from swampy 

 pools near Media, several miles from the places where it had first been 

 observed in 1905. Accompanying it were a few Navicula major and 

 .V. viridis Kutz., together w T ith vast numbers of Closterium sp., long 

 strands of Hyalotheca sp. and other desmids. Preparations were made 



1 Treatment of the Navicula-Pinnularia question herein is that of H. Van 

 Heurck and most recent writers except P. T. Cleve. 



