194 SELECTED NOTES FROM 



a superior layer, covered with fine lines of dots, crossing each 

 other diagonally at a distance apart of about i /30,000th of an inch. 

 The central part and the small marginal spaces at the ends of the 

 radial lines appear to be of solid silex, destitute of markings. 

 The radial divisions range from six to twelve. See Carpenter's 

 'Microscope, 6th edition, p. 350, and PI. I. 



Aulacodiscus orientalis.— Another of the beautiful discoid 

 forms, so called from having " furrows " running from the centre 

 to the margin, at the end of which come i7iflated tubercular pro- 

 cesses, varying in number. 



Triceratium formosum. — The Trtceratia slxq z\?,o another very 

 beautiful class of very varied form ; sometimes they are square, 

 not triangular. The projections at the edges are prolonged in 

 some species into horns ; in others, they are tubercular elevations. 



Pleurosigma formosum.— One of the most elegant of Diatoms, 

 The Pleurosigma are separated from the genus Navicula in having 

 a lateral sigmoid curvature. The strise by which the valves are 

 adorned range from 20,000 to 100,000 to the inch. Pleurosigma 

 formosum is said to have 37,000 for the transverse and 30,000 for 

 the diagonal markings. These are clearly seen by a ^-inch 

 objective. 



Oamaru Selection.*-This slide contains the following : — Aulaco- 

 discus margaritaceus, var. Debyi ; Triceratium Nova Zealandicum ; 

 Stephanopysis valida ; Biddulphia Tuomeyii ; Triceratium glanda- 

 rium ; Triceratium majus ; Triceratium Nova Zealandicum ; Kit- 

 tonia elaborata — this last is one of the special forms of Oamaru 

 deposit. 



Kiver Lea, Freshwater Deposit.— Some of the leading forms 

 are : — Epithemia gibba, turgida ; Navicula gracilis, limosa ; Nitz- 

 sckia angustata, linearis, sigmoidea ; Pinnularia nobilis, viridis ; 

 Pleurosigma attenuatum (abundant), acuminatum, Spencerii ; Stau- 

 roneis Smithii (rare) ; Surirella biseriata bi/rons ; Coscinodiscus 

 lineatus, an intruder. These intrusions can scarcely be avoided, 



* We enumerate the principal diatoms seen on these slides to show what 

 forms are usually found in the various deposits. — Ed. 



