4 DON KIN, ON DIATOMACEiE. 



diatom, as I have ascertained by ample experience in searching 

 after living forms. It is not even a marine species, its 

 habitat being the brackish water of the tidal estuaries, "where 

 it occurs abundantly. On the open shore, free from the 

 influence of streams, its occurrence is very rare and accidental. 



PI. lanceolatum Dr. Arnott considers to be " a form of 

 PL (Bstuarii, Sm., peculiar to clean sand.^^ — ' Micr. Jour.,' 

 vol. vi, p. 197). "These two forms," he says, ''have not 

 been sufficiently isolated to permit any positive deduction to 

 be drawn." This reads somewhat paradoxical; but I must 

 reply, first, that PL lanceolatum is a very much larger form 

 than PL cestuarii, and has not apiculate extremities; the 

 colour of the valve is rich salmon, while that of the latter 

 is bluish inclining to purple ; secondly, that both are found 

 in the typical state developed under the same conditions in 

 the same localities, on the surface of the clean sandy beach ; 

 and thirdly, that I have gathered each form singly in separate 

 localities. Dr. Arnott seems to found his opinion of the 

 identity of these two species on the assertion of Professor 

 Smith, that PL (estuarii is frequently " direct." It is pos- 

 sible, however, that Professor Smith has confounded the two 

 forms together. 



Some observers have objected to Epithemia marina, that it 

 is a Nitzschia ; but with this opinion I cannot agree : it has 

 neither the compressed frustule nor the keeled valve of that 

 genus ; on the contrary, its valve is inflated, and I have been 

 able to detect on it a median line with central and terminal 

 nodules, which is best seen in dry specimens, when the 

 ventral surface of the F. V. is carefully brought into focus 

 under a high power and good illumination. These charac- 

 ters of the valve, taken in connection with the ornamented 

 appearance of the hoop, would prove the species in question 

 to belong either to the genus Amphora or to be a member 

 of a new genus ; to the one or the other of which, it and the 

 following closely allied forms, Nitzschia virgata, Roper, 

 Nitz. Amphioxys, Sm., and Nitz. vivax, Sm., ought to be 

 referred. In all of these the striae are punctate. 



In the first two sections of the following list, I have in- 

 cluded all the species enumerated under Sections I and II of 

 my former paper. 



Section I. — Species described in Professor Smith's Synopsis. ■ 



a. Brackish Water Species. 



Epithemia Musculus, Kiitz. Epithemia Constricta, De 

 „ Westermanii, Breb. 



Kiitz. Amphora affinis, Kiitz. 



