6o Clarence J. Elmore 



6. Eunotia robusta Ralfs in Pritch. Inf., p. /6s. 

 PI. 5, fig. 164. 



Arcuate with nearly parallel margins ; dorsal margin with sev- 

 eral swellings, ventral margin usually without swellings; 48-90/* 

 long, 9-10 /A wide; ends rounded; striations perpendicular to the 

 dorsal margin, 9-10 in 10 fi. 



In San Joaquin River, Stockton, Cal. 



7. Eunotia eruca Ehr. 1844. 

 PI. 5, figs. 165-167. 



Valves arcuate, 48-88 /a long, 8-12 /* wide; apices produced; 

 both dorsal and ventral margins undulate ; striations perpendicular 

 to the dorsal margin, 8-10 in lO/x. 



In San Joaquin River, Stockton, Cal. 



17. Ceratoneis 

 Ceratoneis Ehr. 1840, Emend. Grun. Diat. Insl. Banka, p. 7, 

 J865. 

 Etym., Gr. /ce/oa?, horn. 



Cells single, free ; valves lunate ; pseudoraphe nearer to the 

 ventral than to the dorsal side, the ventral side with a swelling 

 opposite the central nodule ; terminal nodules more distinct than 

 the central ; cells rectangular in girdle view. 



Ceratoneis arcus (Ehr.) Kiitz. Bacill., p. 104, pi. 6, fig. 10. 

 1844. 



Naviciila arcus Ehr. Inf., p. 182, pi. 21, fig. 10. 18^8. 



PI. 5, figs. 168-169; pl- 22, figs. 821-822. 



Valves arcuate, 30-109 /x long, 3-4/* wide, slightly lanceolate 

 with a median inflation on the ventral side ; apices more or less 

 capitate, bent slightly toward the dorsal side; striations finely 

 punctate, perpendicular to the margins, 13-15 in 10 /x. 



In San Joaquin River, Stockton, Cal. 



Family 6. NAVICULACEAE 



Cells free-swimming, stipitate, enclosed in gelatinous tubes, or 

 occasionally adhering in filaments. Rachis containing a median 

 elongated slit (raphe). Valves with transverse striations which 

 are interrupted by the rachis. 



