5i 



k;. — Rays interrupted by smooth or lunate spaces (21). 



20. — Rays uninterrupted by smooth, transverse spaces (1 



31. — Area] stria? forming externally by their union an arched or 

 convex line, limiting (internally) the blank spaces which 

 interrupt^the Rays (43). 



22. — Areal striae forming a straight or concave line, limiting inter- 

 nally the smooth, lunulate spa< C. Graillii, Leud. 



23. — Rays very numerous, fine and close set, radiating and reach- 

 ing to the pseudo-Raphe. Raph. very narrow, linear, 

 parallel-sided. C. Kutzingii,* Harv. and Bail. 



24. — Raphe more or less developed, or else replaced by a mere 

 line (25). 



25. — Areal interstriae, transversely lined. C. Schmidtii, Grun. 



26. — Area without transversely-lined interstriae (27). 



27. — Raphe with a line of granules on each side. 



C. biseriatus, Deby. 



28 — Raphe not bordered by granules (29). 



29. — Rays showing distinct undulations. C. biangu!atus,i Grew 



■Rays without distinct undulations (31). 



•Rays 80 or more in number, valves quadrate. 



C. fluminensis, Grun. 

 Rays much fewer in number (33). 



Raphe trapezoidal, with a granule in each obtuse angle. 



C. socio /is, O. Witt 

 Raphe not trapezoidal (35). 



■ This is the same Diatom as C. Striolatus, Grun., but Kutzingii must 

 have priority. 



t Synonymous with C. Lorent 



icinus, driin. 



