360 CONTRIBUTIONS FROM Mil NATIONAL HERBARIUM. 



Grun. Verh. Zool. Bot. Gee. Wien 12: 512. i s »><i. 0'M< 

 I: y. Irish lead. [1.2:388 not - Van Heur. Treat. Diat. 244. j 



Breb. in pan: \\ . Smith, Synop. Brit. Di 

 mema Ehrenb. in pari Kali- in Pritch. Hist. [nfus. ed. I. 878. pi. 

 is.. I 

 Do tphora Kut W. Smith, Synop. Brit. Diat. 1: 77. pi. L853, inpart. 



in pan. Thwaites, Aim. Mag. Nat. Hist. 11. 1: !7(». /</. /.'./'. //. 

 L848. Van Heur. Synop. />/. 17. J ... 5. 1881. 



.in pan: Scott. Crypt. Fl. 1: 294. 1823, Ralfe, Ann. Mag. Nat 

 Hist. 16: 110. pi. S.f : L845. Van Heur. Treat. Diat. 245./. U - 

 ! Kut Ba ill 103 I 1844, in pan. Van Heur. Synop. 113. 



pi. 17. J L881. Cleve, Sv. Vet. Akad. Handl. 86 a : 125. 1894. Van Heur. 



Treat. Diat. 242./. \t. 

 R< ieheltia Van Heur. Treat. Diat. 243./ ... L896 



\ ictda Bory, m pari: W Smith, Synop. Brit. Diat. L: 16. pi. 16. f. 129. L853. 

 Ki'n/. Bacill. 94. pi. - L844. Donk. Brit. Diat. 42. pi. 



n 12. L872. 

 The separation of the above genera, in whole or in part, from the true Navicula 

 diatoms is generally fell by students to be necessary. Although they have a navicu- 

 loid outline and possess valves that are alike and that bear a raphe divided at the center, 

 they possess -\ era characterisl ics found in do other naviculoid diatoms. The chief 

 characteristic is the elevated, ri< 1lt« --1 i k « • border of silica thai Biirrounds the tw<> halves 

 of ili«' raphe, partly or completely inclosing them and, by its longitudinal extension 

 at the center of the valve where it represents the central noduli , separating the two 

 halves of the raphe farther and farther, until in Amphipleura and Reicheltia the 

 greater length of the valve is traversed by this ridge and the two halves of the raphe 

 are near the apices. It is on the basis of the gradual extension of this ridge and the 

 consequent progressive separation of th< two halves of the raphe thai I have here 

 combined these forms into one genus, as il appears to me there is no distinction between 

 the genera above enumerated except this variable one. Viewed from this stand- 

 point the series would be as follows: I Frustulia Van Heurckia i, where the central 

 extension of the ridge is short and the two halves of the raphe traverse nearly the 

 whole Length of the valve; _ Brebissonia synonymous with Doryphora . where the 

 central extension of the ridge is greater; 3) Berkeleya, where the central exto 

 of the ridge is one-sixth to one-fourth the Length of the valve and the two hal 

 the raphe are correspondingly reduced; l Amphipleura and Reicheltia, in which the 

 centra] extension of the ridge is extreme and the two halves of the raphe very short 

 and near the apices. It Beems to me simplicity is gained by this union, Bince one 

 member of the series runs into another, and especially since t hey are otherwise greatly 

 alike, being characterized by great delicacy of structure with transverse beaded 

 striae of extreme fineness covering the entire valve, except the r\^-. Reicheltia is 

 the most aberrant of this group, its striae being Large, though very finely punctate, 

 and the headed terminations of the divisions of the raphe being peculiar." Still it is 

 bo manifestly a unique Bpecies of Amphipleura that it is difficult to separate it. 



Pfit/er'' brings out the interesting fact that the above differ strikingly from 



Navicula in internal structure, in the process of fission, and in that of conjugation. 



Frustulia rhomboides (Ehrenb.) De Toni, Syll. Alg. 2: 277. L891. Cleve, Sv. Vet. 



Akad. Handl. 26-': L22. L894. 



Navicula rhomboides Ehrenb. PhyB. Abh. Akad. Wiss. Berl. 1841: 419. pi 5. I f. 



15. L843? Kut/. Bacill. 94. pi. 18. f. ,■>. />'■ SO. / ,.. L844? W. Smith. 



i Van Heur. Treat. Dial 243. f I 1-'-, 

 & Banst. Bot. Abhandl. 2: L 871. 



