KONGL. SV, VET. AKADEMIENS HANDLINGAE. BAND. 27. N:0 3. 99 



terminal fissures. Axial area indistinct; central area a broad fascia, widened towards the margins. 

 Striae strongly radiate in the middle, convergent at the ends, 9 to 10 in 0,oi mm. Zonal view of 

 the frustule rectangular with strongly divergent striae. — Alloioneis Stauntonii Gbun. CI. M. D. 

 304. Foss. D. Ost. Ung. p. 142 PL XXX f. 36. Amphora naviculacea Donk. M. J. 1861 p. 11 

 PI. I f. 12? 



Marine, sestuaries: Scotland! 



Ampliora Ehb. (1840). 



The first known species of Amphora is A. ovalis, described as Navicula Amphora by Ehken- 

 BERG 1831. The genus Amphora was established by the same author 1840 (Ber. p. 11). In the 

 »Bacillarien» Kutzing 1844 described 18 species only, but this number was greatly increased by 

 Gkbgoby (Diat. of Clyde 1857), who named 32 new species and first made the distinction between 

 forms with complex and not complex connecting zone. Several other authors have since added 

 new species and in the year 1873 Professor H. L. Smith published (Lens p. 65) a synopsis of all 

 the known forms. By the issue of the plates XXV to XXYHI (1875) and XXXIX, XL (1876) 

 of A. Schmidt's Atlas the number of species was greatly increased. Since then new species 

 have been added, and in the Sylloge of Db Toni (1891) the number amounts to 221. 



An inspection of these species shews that it is impossible to give any diagnosis of the 

 genus Amphora, which is sufiicient to distinguish it from Cymbella. The following seems to be 

 the only possible diagnosis of Cymbella and Amphora together: 



Naviculoid diatoms, with both valves similar and asymmetrical along the longitudinal axis. 



The distinction between Amphora and Cymbella is, so far I can see, no other than the 

 degree of asymmetry; the ventral and dorsal side of Cymbella being in the same plane, but in 

 Amphora in planes crossing each other in an angle, which is variable. 



Amphora and Cymbella are only asymmetrical forms of Naviculae, belonging to different 

 types. There are in the same species gradual passages from perfectly symmetrical to asymme- 

 trical amphora-like forms (as in Trachyneis aspera). In several groups of Navicula more or less 

 asymmetrical forms occur (for instance Pinnularia Stauntonii and others, formerly named Alloioneis) 

 so closely connected with the symmetrical that it would be unnatural to separate them. The 

 asymmetrical form is not a sufficient characteristic for a natural family, but is merely a facies, 

 which may occur in groups of very different types and seem to depend on the method of growth. 

 Amphorae occuring attached to algae and other objects. This genus is in short to be considered, as 

 well as Achnanthes and Cocconeis, as degenerated forms. To trace the origin of these forms is in 

 most cases difficult, as the intermediate passages are lost or unknown, but we may get some ap- 

 proximate knowledge of the original types by the study of the structure of the valve and by 

 comparing it with that of different types of Navicula. 



The Cymbellae appear, to a great extent, to be asymmetrical forms of the section Naviculm 

 lineolatcB, and the same may be the case with the still imperfectly known Amphora labuensis. 



Amphora Clevei is no dbubt nearly akin to the genus Trachyneis. 



Amphora elegans Perag. is with great probability allied to the section Naviculce orthostichee. 



As to the other large number of Amphorae, they may be classed in forms with and with- 

 out longitudinal lines. Those with lines are probably asymmetrical forms of Diploneis or 

 allied genera. There are in some species of this section forms with a structure so closely re- 

 sembling that of Diploneis that the idea of their connection presents itself at once to the mind, 

 notwithstanding the different shape of the valves. In the large Amphora nodosa we have a form 

 with coarse, transverse costae, alternating with rows of ocelli, as in Diploneis Beyrichiana, D. lesi- 



