MANN DIATOMS OF THE ALBATROSS VOYAGES. 241 



which the valves turn vertically downward to form a band, ornamented like the face 

 of the valve with a rugged network; so thai the two valves it placed together form, 

 w n I ion i the connecting girdle, a cylindrical pill box. In this they agree with Meloeira, 

 though <li ffering from thai genus in mode of growth. I have adopted here the generally 

 admiral »lr classification of Rattray, although in this and some other respects il 

 open to criticism, a state of things probably inevitable under any arrangemenl . 



Some of the members of this genus approach, through their markings, Stictodiscue 

 and Bemiptychus Ehrenb., and. through their proces ee Tripodiscue Ehrenb. 

 Coscinodiscus africanus Jan. Diat. Gaz. Exped. pi. S.f. .'. ined. Schmidt, Atlas pi. 



59. f. .'/. 25. De Toni, Syll. Alg. 2: L258. L894. Ratt. Proc. Roy. Soc. Edinb. 



16: 534. L889. 

 This remarkable form shows two sets of border markings; one of fine radial lines, 

 i. c. perpendicular to the margin, the other of strong spirally and obliquely arranged 

 markings, made very prominenl in the above figure by Schmidt. 1 am convinced 

 these latter are an optical illusion. The) are caused by the fad thai the actual 

 herder markings, the fine cross lines, do nol lie parallel on the two surfaces of the 

 border, the upper and under Bides, belonging to the upper and under valves of the 

 fnistule. In other words, the two sets of lines cross each other a1 a very acute angle. 

 This peculiarity is the resull of the excentric arrangemenl of all the markings of the 

 valve. The two foci arc not directly above each other; and tin refore the lines radi- 

 ating from them, including the fine lines on the border, are uol parallel. A.e a con- 

 sequence the false spiral markings appear besl under low powers of magnification 

 or when slightly oul of focus. Under a one-twelfth inch objective and with careful 

 focusing they are not to be seen. 



The curious excentric arrangemenl of the network and the spiral appearance oi 

 the holder seem like an abnormality. Bu1 the specie- is very true to Its type. My 

 specimens come from the same locality as the original, the Galapagos Islands. TIha 

 are another illustration of the value of the diatoms for indicating locality. Castra- 

 cane's "var. rotunda" of this species, though recognized by De Toni, has uothing 

 to recon unci id such an assignmenl except the mere accidenl of an excentric arrange- 

 menl of markings. 



Found at station 2807, Galapagos Islands. 

 Coscinodiscus asteromphalus Ehrenb. Ber. Akad. Wis-. Berl. 1844: 77. 1845; 



Mikrog. pi 18. f. -,-',. pi .;.;. X V.f. 7. 1854. Pritch. Hist. [nfus. ed. I. 828. 1861. 



Grun. Denkschr. Akad. Wien 48-': 78. pl.S.f. 9. L884. Tain. Beitr. Bacill. [Jng. 



1: 7:;. pi. 17. f. 153. L886. Ratt. Proc. Roy. Soc. Edinb. 16: 549. L889. Schmidt, 



Atlas pi 63. 12. 1878; pi. ILL f. a - Cleve A: Moll, type no. 57. 164. 



Jan. Diat. Gaz. Exped. pi If. 9. Van Hem-. Synop. pi 128. f. t-8, 5; pi ISO. 



f. 1-2, 5-6. 1881. De Toni. Syll. Alg. 2: L268. L894. 

 Coscinodiscus omphalanthus Ehrenb. Ber. Akad. Wiss. Berl. 1844: 266. L845. 



Pritch. Hist. [nfus. ed. 1.828. L861. Cleve & Moll, type no. 57, 215. 11. L.Smith, 



Sp. Diat. Typ. uo. 95 (no1 Schmidt. Atlas pi 63. f. .'. 1878): 

 Coscinodiscus oculus-iridis Ehrenb.; Schmidt, Atlas pi. a.!, f. .'>. 1878. 

 Coscinodiscus centralis Ehrenb.; Schmidt. Atlas/*/. 63. f. /. 1878. 



Rattray says. "This species is distinguished by the evident puncta on the mark- 

 ings." I i in many other species share this character, as C. marginatum Ehrenb. and 

 C. robustus ('.rev. Kali's say-.'' "It di ffers from the other species with stellate umbili- 

 cus by its minutely punctate cellule-." These two distinctive characters should be 

 taken together. 



Found ai stations 2929, 3570, 2287H, 3635H, 1023H, 1025H, off California to Bering 

 Bea. 



oCastr. Hep. Voy. ('hall. Bot. 2: 159. pi :;./. 3. 1886. 

 i> Pritch. Hist. Inftis. ed. I. 828. L861. 



31713 vol 10, pi 5 07 3 



