\I\NN DIATOMS OF THE U^BATROSS VOYA< 233 



c. Frustule a box, with zonal diameter generally shorter, sometimes slightly 

 longer, than the valval diameter; valve generally oval, sometimes p 



nal, circular or semicircular; unipolar, bipolar, or multipolar, each pole 

 represented by an angle or (in Chaeti a horn or spine or by both 



gles and horns. Biddi i ph i \ i 



a. Horns much longer than the frustule, nol tipped with a claw; frustulee 



in chains; valve circular oroval. Chaeto< 

 I*. Horns generally shorter than the frustule; when longer, only slightly so and 

 then lipped with a claw. Biddi i phie \i 



a. Valve tripolar to multipolar; angles not bearing dome-like protrusions 



orhorns; do1 tipped with a claw. Trigonhnae. 

 Valve strong; marking distinct; no central erecl spine. 



289 

 Valve delicate; marking delicate; a central erect spine. 



Ditylum p. 2 



b. Valve generally bipolar, sometimes tripolar to multipolar; each angle 



bearing a dome-like protrusion orahorn; nol tipped with a '-law. 

 Biddulphia \ 



c. Valve unipolar, oval; frustule having zonal diameter longer than valval; 



valve massively sculptured, tmsymmetrically elevated, tsthmiinae.) 



1st fun; 'I p. 311 . 



d. Valve bipolar, tripolar, orquadripolar, each anglehavinga long vertical 



horn tipped with a claw; or in the bipolai form either as described or 

 having the angles oi only one valve turned vertically upward into 

 short-pointed ends without claws. Hemiaulinae. 



Frustule in zonal view not concavo-convex, but having two similar 

 valv< s; valve hi polar, tripolar, or quadripolar, each angle having 



along vertical horn tipped with a claw Hemiaulus p. 312). 



Frustule in zonal view strongly concavo-convex; the apices of the 

 concave valve beingjsharply turned up into a short point destitute 

 of a claw; center of this concave valve raised intoa strongdome, 

 lackingon the convex valve; in valval view the dome is seen to 

 be imperceptibly merged into the rest of the valve, not si -pa rated 



from it by a strong rectangular ridge Ploiaria p. 313 . 



i. Horns rudimentary, reduced to low domes, or wanting; frustule in zonal 

 view having a rectilinear outline; internal septa massive, with en] 

 ends. Ana i leae. 

 Internal septa straight, except at the tip, which is sharply bent toward 

 the center of the frustule and enlarged into a bulbous end. bo that 



septum resembles a music note Terpsinot p. 314 . 



Interna! septa not straight, beginning as transverse septa on the valves 

 near their extremities, pn < eeding vertically downward parallel to the 

 zonal axis, then twice bent and extending parallel to the longitudinal 

 axis to near the center of the frustule, similar to the internal septa in 

 Gramma tophora, the end- straight and moderately enlarged. 



. 315 . 

 d. Horn.- wanting; valve without interna! micircular, broader than 



1 < > t i ■_-■ : frustule in zonal view cuneate. Hemtdisceae . //■ 

 D. Valve narrow or broad spindle-shaped; ends elevated or knobbed; markii 9 



erally radial ; center of valve usually bearing a massive process, shaped like the 

 Greek epsilon and interlocking with the : the next valve, thereby 

 uniting the frustules into chains. Rutelarioideae R • i p. 317). 



