■p. ^ ,- ^,- ..^- .-,^ 



MANN DIATOMS OP TITE ALBATROSS VOYAGES. 233 



C. Friit^tule a box, with i^onal diameter gouerally shorter, sometimes ;shghtly 

 longer, than the valval diameter; valve generally oval, sometimes poly- 

 gonal, eireular or semicircular; uniiK>lar, bipolar, or multipolar, each pole 

 represented by an angle or (in Cbaetoceros) by a horn or spine or Ijy both 

 andes and horns. (BiPDULPTrioiDEAK,) 



C5 



a. Tlorns much longer than the fruslule, not tipped with a claw; frustules 



iji chains; valve cin^ular or oval. (Cha-etockk^a^). Chaetoceros (p. 285)* 



b. Tlorns generally shorter than the frustule; when longer, only diglitly so and 



then tipped with a claw. (Biddulpiiikae.) 



■ 



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



or horns; not tipped with a claw. (Trigoniinae.) 



Valve strf)ng; marking distinct; no central erect spine. 



Trigonium (p. 289). 



Valve delicate; marking delicate; a central erect spine. 



Dityluvi (p. 296). 



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



bearing a dome-like protrusion or a horn; not tipped with a claw. 

 _ _ _ Biddalphia (p. 298 



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



valve massively sculpt ured , unsymmetrically elevated. (Isthmiinae.) 



Isthmia (p. 311). 



d. Valve liipolar, tripolar, orquadripolar, each angle having a long vertical 



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

 having the angles of only one valve turned vertically xipward into 

 short-pointed ends without claws. (Hemiaulixae.) 



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

 valves; valve bipolar, tripolar, or quadripolar, each angle having 



along vertical horn tipped with aclaw Ilerniaulas (p. 312). 



Frustule in zonal view strongly (*oncavo-convex; the apices of the 

 concave valve heing^sharply turned up into a short point destitute 

 of aclaAv; center of this concave valve raised into a strong dome, 

 lacking on the convex vaUe; in valval view the dome is seen to 

 be imperc^eptibly rnerg(Ml into ttn.' rest of the valve, not separated 



from il by a strong rectangular ridge Ploiaria (p. 313). 



c. Horns rudimentary, reducH'd to low domes, or wanting; frustule in zonal 

 view having a re<*tilinear outline; internal septa massive, with enlarged 

 ends. (AxAULKAE.) 



Internal s<^pta straight, except at the tip, whieh is sharply bent toward 

 the ctniter of the frustule and enlarged into a bulbous end, so that each 



septum r(\sembles a music note Terpsinoe (p. 314). 



Ijiternal septa not stnught, beginning as transverse septa on the valves 

 near their extremities, proceeding vc^'tit^ally downward parallel to the 

 zonal axis, tlu^n twice bent and extending parallel to the longitudinal 



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

 Grammatophora, the ends straight and moderately enlarged. 



Porpeia (p. 315). 

 d. Horns wanting; valve withont internal septa, semicircular, broader than 

 long;frustide in zonal view cuneate. (JIemwisceae) .Ilemidiscus (p. 316). 

 D. Valve narrow or broad spindle-whaped; ends elevated or knobbed; marking gen- 

 erally radial; center of A^alve usually bearing a massive process, shaped like the 

 Greek epsilon and interlo( king with th<i process of the next valve, thereby 

 uniting the frustules into chains. (Rutilahioideae) Rutilaria (p. 317). 



