r H 



MANN DIATOMS OF THE ALBATROSS VOYAGES- 363 



These he called Dunkinia.^ The third genus to be separated was Hhuicosigiua 

 by Grunow,?^ including all species with strongly bent frustules (seen in zonal view) 

 and with valves sometimes^ though not always, dissimilar. These distinctions have 

 been accepted by Van Ileurck, Peragallo, and De Toni. Cleve rejects them, except 

 Toxonidea, and accepts this, as he admits, on dubious grounds. I think nothing is 

 gained by breaking up the generic unity of this sharply marked genus. The char- 

 acteristics, as Cleve points out,*" are variable in each of the above cases. For sub- 

 generic division they can be, at least at present, made use of; but beyond this they 

 only increase the difficulty of assigning diatoms that have the clear Gyrosigma quali- 

 ties. 



Cleve has, however, gone further than others toward ol)literating the worth of this 

 genus by dividing it into two genera on the sole basis of the direction of the striation. 

 He includes all forms witli transverse-longitudinal striae in Gyrosigma (Ilass.) Cleve, 

 and the others, with striae in three directions (excepting Toxonidea) in Plenrosignui 

 (\V, Smith) Cleve. It is probably true, as he says, that there are no transitional 

 forms between these two kinds; indeed, it would not be easy to conceive how there 

 could be, for lines iji two directions could hardly change to lines in three directions 

 without assuming new angles, and only one of the three lines could possil)ly remain 

 in the original direction uf one of the two lines; and this is just what we find, both 

 the two-line and three-line forn^is having one of the lines transverse. The lack of 

 transition is, therefore, to my mind an empty argument. If, now, we look at the 

 striking forms, called by Ralfs Donkinia, a geims rejected by Cleve, we find species 

 of both two-line and three-line sculpture that are far too close to put into separate 

 genera, on any reasonable interpretation of a genus; thus D. recta (Donk.) Grun. 

 and D, carinata (Donk.) Ualfs.f^ Whoever also compares such two-line forms as G. 

 {PleuTosigma) litiorale (W. Smith) Griff. &: Henf. and G. {Pleurosigma) acvmnatum 

 (Ktitz.) Grun. with such three-line forms as <7. (Pleurosigma) latum. Grun. and (7. 

 {FlcuTosigma) ajjinc Grun, must see that it is artifirial to place them in two genera. 

 I do not therefore look upon Clove's division of this genus as having the merit of the 

 earlier ones. 



Gyrosigma aestuarii (lircb.) Griff. & Ilenf. Micr. Diet. ed. 3. 35G. pi. 11. f. So. IS7o. 

 Naiicula aestliarii'[^rQh.\ Klitz. Pp. Alg. 890. 1840. 

 Pleurosigma aestuarii \\ . Smilli, Synop. Brit. Diat. 1: 65. pi. SI. f. 275. 1853. Cleve 



& Grun. Sv. Vet. Akad. IlandL 17-: 52. 1880. Pcrag. Le Diatomiste V': 12. 



pi 5./ 12^13, 15. 1891. Cleve, Sv. Vet. Akad. Handl. 26-: 42. 1894. Pritch. 



Hist. Infus. ed. 4. 91G. 18G1. Kabh. Fl. Eur. Alg. 1: 2M. 1864. Griff. & TJonl. 



Micr, Diet. ed. 3. pi 15. f. 35 (/. 3Sc?). 1875. Van Hour. Synop. j^l ^S.f, 8. 1881, 



H. L. Smith, Sp. Diat. Typ. no. 394. 1874 (not Cleve, liih. Sv. Vet. Akad, 1'^: 



13. pi 2,f, 19. 1873= 7^. normanii Halfs). 

 Pleurosigma amjulatiini W. Smith, variety; Van Heur. Synop. 115, 1881; Treat. 



Diat. 251. pi. G.f. 258. 1890. Do Toni, Syll. Alg. 2: 232. 1891. 

 Plfurodgma candidavb Schum. Schrift. Phys. Okon. Ges. Konigsb. 8: 59. pi, 2,f. 



57. 1807. Perag. Le Diatomiste 1^-': 12. pi. 5.f. 11. 1891, 



The desire of II. D. Smith, Van Ilcurck, and De Toni to make this a varit^ty of 

 P. angulatam W. Smith is not ttj l)e comnuaidcd. Though small<T than the lal-Lcr, 

 the markings are decidedly coarser, the ends narrower and less gracefully tapered, 

 and in the type form slightly but sharjdy bent sid(nvise. 



Found at station 2823, Gulf of California. 



aPritch. Hist. Infus. ed. 4. 921, pi. S.f. 49. LSGl. 



2>Sv. Vet. Akad. Ilandl. 17^: 58. 1880. Le Diatomiste l-^-'; 33. pL 10, f. 2-S. 1891. 

 ^Sv. Vet. Akad. Handl. 26-: 32, 112. 1894. 



c^ Trans, Micr. Soc. Loud. n. s. 6: pL S.f. 5, 6. 1858. Le Diatomiste 1-* ■': pi. U.f. 

 6, 8. 1S9I. 



