412 



CH^TOCERE^;. 



Tribe XIX. Ciletocere.e. 



Frustules 



consisting 



of 

 numerous 

 imbricate 



or 



juxtaposed 



hoops. 



Frustules 



not 

 consisting 



of 



numerous 



hoops. 



Valves 

 symmetri- 

 cal. 



Valves 

 asymmetri- 



cal. 



Valves 

 bordered 



with 



extremely 



long 



spines. 



Without awns, sometimes a circlet of marginal 

 dots ..... 



I 



| Furnished with numerous more or less developed 

 awns ..... 



Valves elliptic, furnished with two awns 



k Valves round, with two long spine-like horns 



Valve showing an undulation terminating in a 

 rudimentary mucro, placed laterally 



| Valve calyptriform, showing a more or less 

 [ developed mucro, generally ending in a seta . 



Spines not arranged in a circle on the margin of 

 the valve .... 



No very 



long 



marginal 



spines. 



Spines 



arranged 



in a circle. 



A long 

 central 

 spine. 



f Spines forming a flat corona (rays) 



round the valve 

 1 



i_ Spines erect 



f Valve angular, very slightly sili- 

 cious ; spine setiform 



Valve rounded, with two biddul- 

 phiform marginal elevations 

 and with a central spine ter- 

 minating in a forked claw 



Valve with a cylindrical central eleva- 

 tion, bordered with very robust spines 



Dactyliosolen. 



Lauderia. 



Attheya. 



Peragalloa. 



Guinardia. 



Rhizosolenia. 



Chsetoceros. 



Bacteriastrum. 

 Corethron. 



Ditylum. 



Syndetoneis. 

 Pyrgodiscus. 



Frustules compressed, with su- 

 tural portion narrow ; horns 

 often branching or bifurcate, 

 sometimes mucronate. Valves 

 sometimes short and obtuse, at 

 other times furnished with 

 short scattered spines 



Fiustules elongated, with mucro- 

 nate horns. Generally one of 

 the valves with only one horn 

 or process and the other with 

 two 



Valves dissimilar, furnished with rather short setiform spines . 



Valves similar, smooth or hyaline, fossil, without spines, often 

 united by a constricted central part 



Valves furnished with small scattered spines 



Dicladia. 



Syringidium. 

 Hercotheca. 



Goniothecium. 

 Chsetoceros. 



I. RlIIZOSOLENlE.E. 



imbricate or juxtaposed hoops (annuli). 



Frustules consisting of numerous 



The Rhizosolenieae are the subject of an excellent monograph by Mr. H. 

 Peragallo inserted in Le Diatomiste for 1892, to which we refer the reader for 

 a complete examination of this sub-tribe. 



