200 A. A. C. ELIOT MERLIN ON SOME NEW DIATOMIC STRUCTURE 



Van Heurck). The diameter of these primaries was afterwards 

 carefully measured and proved to be 0*0001122 in. when corrected 

 for antipoint. Subsequently I re-examined many objects familiar 

 to me with my older objective, particular attention being given 

 to such as possess extremely elusive features just within the grip 

 of that lens. In every case, without exception, the observa- 

 tions previously recorded were confirmed by the new objective, 

 features previously extremely difl&cult being found comparatively 

 easy, while various new structures, unsuspected before, have been 

 discovered. Amongst these I venture to bring the following to 

 your notice : 



Craspedodiscus coscinodiscics. The secondaries of this particular 

 specimen were doubtful until re-examined with the recent lens, 

 which exhibits them quite certainly. 



JEpitheniia turgida. The primaries prove to be irregularly 

 cruciform in shape, somewhat of the Arachnoidiscus type. These 

 require high magnification (about 3,000) and very perfect defining 

 power to properly reveal their true nature and shape. 



Cymbella gastroides Kiitz. Primaries rectangular in shape, 

 divided and broken up into secondaries. 



Gomphonema geiniinatum Ag. Secondaries closely resembling 

 the foregoing. 



Stictodiscus areolatus Grun. (0am aru). Exhibits a delicate but 

 not particularly difficult network on the lower surface of the 

 valve. A fine dotted structure can be seen on the under edge 

 of the rim of this specimen. 



AulacodisGus Janischii Gr, and St. (Oamaru). This exhibits a 

 very distinct and obvious "veil." Should prove to be within the 

 grasp of most good cheap oil-immersion lenses. 



Endictia oceanica Ehr. (fossil, from Peru guano). This pos- 

 sesses easy secondary perforations plainly seen in balsam. 



All the foregoing observations were made with working aper- 

 tures varying between 1"3 and 0"95 N.A. In no instance was 

 oblique light or a smaller illuminating cone employed. 



There can apparently be little doubt that few, if any, diatomic 

 valves possessing medium-sized primary perforations have such 

 passages into the interior of the organism unobstructed or un- 

 protected by caps pierced by finer holes. The limit of this 

 capping we are at present unable to discover, but it woiild seem 

 probable that species possessing very fine primaries, such as the 



