PECULIAR FORMS OF NAVICULA. 285 



the species of Naviculae are already so numerous. But my 

 opinion has been greatly modified by the recent discovery of 

 several forms in which the costate stria? of Pinnularia are 

 found combined with the moniliform structure which is 

 characteristic of Navicula. 



For the material in which these forms are found I am 

 indebted to the kindness of Capt. Chimmo, of H.M.S. 

 Nassau, who states that he raised it from an extinct volcano 

 from a depth of 300 feet, in the Island of Cagayan, Sulu 

 Archipelago, north of Borneo, and remarks that the water 

 was salt, and the mud yellow, and emitting a sulphurous 

 smell. The mud contained a very large per-centage of 

 calcareous matter, so that, after treatment with hydrochloric 

 acid, the residuum was very small, but having a considerable 

 number of interesting diatomaceous forms mixed up with a 

 relatively large p>roportion of sponge spicules, and radiolarian 

 organisms. 



At present I mean to confine myself to those forms of 

 Navicula which exhibited the double structure already 

 noticed. 



Navicula Chhmnoana (P\ate^lll,^g.l) . — Valve constricted, 

 somewhat abruptly rounded off at the ends ; length 'OOSS ; 

 greatest breadth "OOSO; breadth at the constriction "0017. 

 Central nodule square, median line slightly sigmoid, and 

 having a narrow unstriatcd band on either side ; costee 

 distant, narrow, slightly radiate towards the apices, and 

 nearly parallel at the middle ; waved as they approach the 

 free median band, on which they form a crenulated border ; 

 the space between the costa? filled up with a single row of 

 large oblong dots, Avhich run from the outer margin of the 

 valve, and do not extend quite so far as to half the length of 

 the costse. 



Navicula Sulu€?isis (fig. 2). — Valve constricted, gently 

 rounded off towards the somewhat lanceolate apices ; length 

 •0076 ; greatest breadth "0017 ; breadth at the constriction 

 •0013. Central nodule square, median line slightly sigmoid, 

 and having a narrow unstriated band on either side; costae 

 distant, narrow, slightly radiate towards the apices, and 

 nearly parallel to the middle ; waved as they approach the 

 free middle band, on which they form a crenulated border. 

 The sjjaces between the costse for about one third their length 

 filled with a single row of oblong dots. 



This form in many features strongly resembles N. Chim- 

 moana, but is readily discriminated by the following 

 characters : It is much longer and narrower, more graceful 

 in its outline, and the border occupied by the moniliform 

 dots is much narrower. 



