DENTICULA. 



351 



GENUS 65. DENTICULA KUTZING, 1844. 



Z'J 



enables 

 various 



Valves more or less lanceolate, 

 fusnished with a carina and transverse 

 costae, between which punctate striae 

 can be seen. Frustules solitary or in 

 short chains, with girdle face quad- 

 rangular, showing the capitate apices 

 of the costae. 



A dozen species of Denticula are 

 known, and these are scattered throughout 

 the world. The presence of a carina 



the Denticula to be associated with the Nitzschia, and with this genus 



authors have arranged them. 



Fig. 103. 

 Denticula elrmns. 



ANALYSIS OF SPECIES. 



f Girdle face very broad, showing costas with capitate apices ; valves with 



obtuse apices, carina indistinct, strire 14 to 17 in 1 c.d.m. . . D. elegans. 



j Girdle face broad. Valve with apices subacute, carina conspicuous ; striae 



i, fine, about 17 in 1 c.d.m. . . . . . D. tenuis. 



I Girdle face very narrow. Valves with apices acute, carina invisible ; stria; 



(^ very fine, about 30 in 1 c.d.m . . . D. subtilis. 



D. elegans Kutz. (Baa, p. 44. pi. 17, f. 5; H.v.H. Atl., pi. 49, 



f. 14, 15*; in Types Nos. 48 and 257; D. ocellata IV. Sm.), plate 31, 

 fig. 860. 



Valve linear, lanceolate, with apices obtuse rounded, carina obscure, 4 or 

 5 costas in i c.d.m.; striae robust, strongly punctate, about 17 in 1 c.d.m. 

 Girdle face very broad, rectangular, with rounded angles, showing the apices 

 of the costas, strongly capitate. Length, 2 to 3 c.d.m. Breadth of girdle 

 face, about 1 c.d.m. 



Fresh water (on rocks, etc.). England, Scotland (Balfour), Ireland (O'Meara). 



var. thermalis (D. thermalis Kutz.; H.V.H. Atl, pi. 49, f. 17, 18*), 

 plate 31, fig. 861. 



Valve somewhat broader, with apices less obtuse. Striae, 14 in 1 c.d.m. 



Thermal waters. Sweden (Lagerstedt). 



