RECENT RESEARCHES IN THK DIATOMACEiE. 87 



According to Kiitzing, William Smith, and Professor H. L. 

 Smith, Amjihipleura is assigned to a jjosition more or less 

 intimately associated with the Naviculacecs. 



The two next groups, Plagiotrojndece and Amphitropidece, 

 axe intimately associated with the genus AmpMprora, Ehr., 

 which has been regarded as nearly related to the Navicu- 

 lacece, but the allied forms are by Plitzer associated with the 

 Nitzschiea. The character which these four groups possess 

 in common, and in consequence of which they are so inti- 

 mately associated by that author, is the development of 

 certain longitudinal lines into more or less prominent keels. 

 Whether this characteristic should be deemed a sufficient 

 reason to justify the arrangement referred to may be con- 

 sidered as liable to doubt; it is, however, important to keep 

 this common feature in view. 



Let the author now speak for himself — 



Amphipleurecs, Grun. 



This embraces two genera, Amphipleura, Kiitz., and 

 Berkeleya, Grev. The only European fresh-Avater form of 

 this group, distinguished from the Naviculem by the deve- 

 lopment of the central nodule on one longitudinal line, and 

 the three keels of the valve — namely, Amphipleura pellucida 

 (Ehr.) Kiitz. — possesses two endochrome-plates lying on the 

 girdle-bands. A central plasm-mass is also observable. In 

 the process of constructing auxospores, only Berkeleya Dill- 

 wynii (Ag.), Grun., has been observed by Lilders. For this 

 purpose many cells unite in a common gelatinous envelop- 

 ment on the extremities of the tubes, or smaller expansions 

 arise on the sides and middle of the tubes ; two mother cells 

 then develope two auxospores. 



" The structures described by Kiitzing, Bac, p. 112, t. 

 23, f. ii, 2 a b c, as the fruit of Berkeleya tenuis (Kiitz.), 

 appear to me," adds Pfitzer, " not to belong to the Bacilla- 

 riacc(S at all.''' It appears then that, so far as the internal 

 structure of the cell is concerned, Amphipleura bears a 

 strong resemblance to Navicula. 



In case the character noted by Pfitzer — namely, the 

 development of a central nodule on one median line, by 

 which I understand its occurrence on one valve and not on 

 the other — be sustained by fact, the position of Amphipleura 

 will be seriously affected. In special reference to this 

 subject I have examined very many specimens of Amphi- 

 pleura pellucida and could observe no trace in any of a 

 central nodule. 



