OF THE FRAGILARIEJi;. 



773 



FAMILY IA\— FKAGILARIEJE. 



Fiiistiiles straight, free, or affixed by one augie of the basal friistiiles, in 

 front view linear, in lateral view compressed, and striated or smooth, with a 

 central nodule ; stride or costce pervious. " The members of tliis family are 

 allied in the genus Denticula to Surirella and IS'avicula ; in the genera Odon- 

 tidium and Fragilaria to Himantidium, Diadcsmis, and the Meridie^e, and in 

 Diatoma to Grammatophora and Tabellaria." (Kiitzing.) '' The character by 

 which these genera are collected together into one family is the conformity of 

 the two primary surfaces ; nor do I know how the genus Meridion is excluded 

 even by the minutest characters." Kiitzing, indeed, " cites the affinities with 

 Himantidium among Eunotiese, with Diadesmis among the Na\dcul8e, and 

 Avith the various genera of Stiiatelleoe. The relation appears to us rather 

 one of analogy than of affinity, being the polyparifonn association of many 

 individuals." (Meneghini.) Under Meridiere we state the reasons which 

 induce us to dissent from Meneghini's opinion respecting the position of 

 Meridion. The striae and costae are usually continuous across the valve ; and, 

 indeed, Kiitzing makes their jDcrviousness a distinctive character, separating 

 the Fragilaiiece from the Surirelleae. We regard Meridion as far more nearly 

 allied to some genera belonging to the latter family than to the genera 

 mentioned by Meneghini. 



Genus DEo^TICULA (K.). — Free, sohtary, or binately conjoined, rarely 

 more ; valves with pei^ious costae, which appear in front view like marginal 

 puncta. Fresh water. Denticula differs from Odontidium in not forming a 

 filament, and also, according to Professor Smith, in ha\ing conspicuous striae, 

 which are wanting or obscure in Odontichum, and from Fragilaria by its 

 strongly marked costae, which Kiitzing regards as always pervious. 



Denticula tenuis (K.). — Front view I elliptic, with 12 to 13 fine striae 



linear vvdth punctated margin ; valves 

 narrow lanceolate, with 10 or 11 trans- 

 verse cost^ in 1-1200". KB. p. 43, 1. 17. 

 £8. Europe. 1-1080". 



D. friyicla (K.). — Front view linear, 

 with finely striated margins ; valves li- 

 near lanceolate, vvith 11 or 12 cost£e in 

 1-1200". KB. p. 43, 1. 17.. f 7. Europe. 

 Smaller than B. tenuis. 1-1200". 



D. thermalis (K.)- — Front view oblong 

 or trapezoid, with beautifully punctated 

 margins ; valves lanceolate, with 7 or 8 

 costaj in 1-1200". IG3. p. 43, 1. 17. f 6. 

 Italy. 1-6G0". 



D. eJegans (K.). — Front view linear 

 oblong, M-ith obtuse angles and gland- 

 Hke marginal puncta ; valves lanceolate, 

 with 6 costfB m 1-1200". KB. p. 43, 

 t. 17. f 5. Germany, (ni. 4.) 1-600". 



D. ohtusa (K.). — Front view linear, 

 with striated margins ; valves lanceolate, 

 with obtuse ends, and 11 costas in 

 1-1200". KB. p. 4:3, 1. 17. f. 14; SBD. 

 i. p. 19, pi. 34. f 292. Europe. 1-336". 



D. crassula (Niigeli). — Front view 

 oblong, with punctated margins -, valves 



m 

 1-1200". Nag. in KSA. p. 889. = 

 I), injlata, SBD. ii. p. 20, pi. 34. f. 294. 

 Europe. 



D. acuta (Rab.). — Front \iew mostly 

 cuneate ; valves slender lanceolate, with 

 6 or 7 costse in 1-1200". Rab Diat. 

 p. 33, 1. 1. £ 8. _ Persia. 



D. lauta (Bail.). — Front \iew linear, 

 with gland-like marginal pmicta ; valves 

 linear lanceolate, with obtuse ends and 

 distant costae, which terminate in mar- 

 ginal bead-like dots. BMO. ^. 9, £ 1. 2. 

 Fossil. Suisim Bay, California. 



D. ocellata (S.). — Front view linear, 

 truncate, with conspicuous foramina- 

 like marginal puncta ; valves linear 

 elliptic, with 10 costae in -001". SBD. 

 ii. p. 20. St. Abb's Head. The frus- 

 tules in the front view closely resemble 

 small specimens of Epithemia Argus. 

 The extremities of the costae or canali- 

 cidi appear as circidar foramina on the 

 f. v., and the costae on the side view" 

 also give an ocellated appearance to 

 the valve, S. 



Genus PLAGIOGRAMMA (Grev.) (Heteromphala, E.). — Frustulcs qua- 

 drangidar, united into a short fascia ; valves with two or more strong, pervious 



