OF THE FRAGILARIE.E. 



775 



Doubtful or insufficiently knomn 

 Species. 



P. kevis (Greg.). — Front view witli 

 slightly but sharply dilated ends and a 

 minute prominence in the middle of each 

 margin ; costte two ?, striae delicate^ about 

 48 in -001". = Denficula IcBvis, Greg Dial 



of Clyde, p. 22, pi. 2. f. 33. Scotland. 

 Side view unknown. 



P. Himanticlium (E.). — Front view 

 eight times as long as broad, with the 

 rounded apices slightly 3-lobed, costse 

 two ?, margin striated. = Heteromphala 

 Himantidium,'EP\BA.. 1858, p. 13. ^^gean 

 Sea. Side view unkno^Ti. 



Genus ODONTIDIUM (K.). — Fmstiiles united into a filament; lateral 

 view linear elliptic or cruciform, with pervious costae. " The Odontidia are 

 merely" a filiform series of Denticulne." (Menegh.) Like Denticula, this genus 

 is distinguished from Fragilaria by its strongly-marked costae, which appear 

 in the front view like marginal i^uncta. The filaments are usually extremely 

 fragile, and when broken up the frustules scarcely differ from those of 

 Denticula. Smith says, " It must be acknowledged that there is little to 

 separate these genera ; and I should be disposed to unite the two, were there 

 not in the general habit of the living frustule characters which enable the 



observer to assign them to their respective genera It may be left to 



futiu^e observers to consider whether they may not without inconvenience be 

 united." 



Odoxtidii-im mesoclon (K.). — Has 

 shorter and subquadi'ate frustules, with 

 from two to four transverse costse. The 

 last character, however, is so inconstant 

 that, although Professor Smith adopted 

 it in his definition, almost every frustule 

 in his figm-es has a greater nmnber. O. 

 c/laciale often has trapezoid frustules and 

 5 or 6 costte, whilst O. turgidulum is in- 

 termediate between those forms and the 

 normal frustules in length and number 

 of costae. 



0. hyemale (Lyngb., K.). — Front view 

 with bead-like marginal pimcta ; valves 

 elliptic-oblong or elliptic-lanceolate, ob- 

 tuse, with conspicuous costae. KB. p. 44, 

 t. 17. f. 4; SBD. pL 34. f. 289; Fragi- 

 laria hyemalis, Lyngb. t. 63 ; F. con- 

 fervoides, GBF. ii. p. 403 ; F. striata, 

 EA. p. 127; Odontidium turqidulum, KB. 

 t. 17. f 2 ; F. turyidulwn, E Inf. ; Odo?i- 

 tidium qlaciale, KB. ; O. mesodon, KB. 

 t. 17. £ 3 ; SBD. ii. p. 16. Common. 

 Europe, Asia, Australia, and America, 

 (xiii. 24, 25.) Odontidium hyemale is 

 easily distinguished from other filamen- 

 tous Diatoms by its exceeding fragility, 

 minute terminal pmicta, gland-like mar- 

 ginal ones, and the conspicuous costae of 

 the valves. The frustules var^^ much 

 in length and in the number of their 

 costae ; and several species have, we be- 

 lieve, erroneously been constituted upon 

 these characters. We do not hesitate 

 to unite them, confirmed in our opinion 

 by the doubts expressed respecting 

 their distinctness bv the late Professor 

 Smith. 



0. Bogotanum (Rab.). — Ver}- small ; 

 valves oblong, with rounded ends, and 

 from 2 to 4 very broad transverse costae. 

 Rab Diat. p. 34, t. 2. f. 8. Bogota. Ap- 

 parently a state of O. hyemale. 



0. capitatum (Rab.). — Foiu* to six 

 times as long as broad; valves lanceo- 

 late, constricted beneath the capitate 

 apices ; costae 6 or 7 in 1-1200". Rab 

 Diat. p. 34, t. 10. f. 17. = O. chamocepha- 

 lum, Rab D. p. 34, t. 10. f. 16 ; Fragi- 

 laria? capitata, EB. 1853, p. 527; Microg. 

 pi. 35 A. 12. f. 2 ; F. ? leptocephala, E /. c. 

 p. 527 ; Microg. pi. 35 a. 12. f. 3. Europe, 

 Persia, and America. 



O. nodulosum (E., K.). — Frustules 

 narrow linear, twelve times as long as 

 broad; valves narrow linear, nodidose, 

 constricted beneath the capitate ends; 

 stri.'B 18 in 1-200". KSA. p. 13. = Fra- 

 gilaria nodulosa, EB. 1844, p. 267. Kur- 

 distan. 



O. jnnnatum (E.,K.). — Frustules three 

 to six times longer than broad ; valves 

 with rounded, not attenuated, ends, 

 and 25 strong strige in 1-1200". KSA. 

 p. 13. = Fragilaria p>innata, EB. 1844, 

 p. 202 ; Microg. t. 35 a. 22. f. 8. Ant- 

 arctic Sea. 



O. minimum (Nag.). — Very small; 

 valves trapezoid, \\dth acute apices and 

 very faint, nearly obsolete transverse 

 striae ; fr-ont view quadrate, with margi- 

 nal puncta. KSA. p. 889. = O. Salishur- 

 gense, Rab D. p. 38, t. 2. f. 7. Em-ope. 



O. rotundatum (E., K.). — Frustules 

 often nine times as long as broad ; 

 valves linear, with rounded ends, and 



