246 CONTRIBUTIONS PROW mm NATIONAL HERBARIUM. 



beads; belon this double-marked outer plafe 

 plate regularly dotted or perforated? . the dotting appearing through the bosses and 

 giving a shadowy granular appearance to the whole valve; rim. or margin 

 of juncture of the two valves, hyaline (not Been in the accompanying figure, being 

 • focus . 

 1 diameter of \ alve, 0.078 nun. 



I coi tne doubt in referring my form to this genus; though its resemblance 



makes me prefer to classify h here rather than accept tin- less advisable alternative 



iting a im-w genus for It. The correctness of placing ii here is rendered more 



probable by its m-ir resemblance to Stephanos i h pecially the last 



My Bpeciee differs from that of Grunov* in everything except the sec lary 



punctation; in the large number of knob-like processes, toward the margin filling 

 ;ill the interspaces, in the evident hyaline border, in tin- absence of "two t" five 

 apines remote from the center." < >i" Grunow'a figure which most nearlj resembles 

 tin- Bpeciee, namel) . figure 30, he »j b: ■ Fig. 30. Form ohne Stacheln, fraglich hieher 

 gehorend. 



Type in the (J. S. National Museum, No. 5901 L9, from station 2807, Galapagos Islands, 

 April l. L888; 812 fathoms, bottom of lobigerina ooze and coral mud. 



COSCINODISCUS Ehrenb. 



kus Ehrenb. Phys. Abh. Akad. Wise. Berl. 1838: L28. L840. Ratt. 

 Pro* Roy. Soc. Edinb. 16: 149. L889. DeToni, Syll. Alg. 2: L200. L894. 

 Symbolophora Ehrenb. in part: Ber. Akad. Wise. Berl. 1844: 205. 1845. 



tya Ehrenb. Ber. Akad. Wiss. Berl. 1845: 71. L846? 

 Odontodiscus Ehrenb. Ber. Akad. Wiss. Berl. 1845: 72. L846. 

 Heterostephania Ehrenb. Mikrog. 15. pi. 85A. XI II B. f. .. 5. L854. 

 Cestodiscm Grev. Trans. Micr. Sue. Lond. n. b. 13: 48. pi 5./. 8, 9. L865. 

 Cosmiodticw Grev. Trans. Micr. Soc. Lond. n. b. 14: 79. pi. 8.f. ii 13. 

 Stoschia Jan.; Van Beur. Synop. pi. 128. f. 6. note. i vs i. 

 Janischia Grun. ; Van Beur. Synop. pi. 95. f. 10 11. 1881. 

 l/. opodiscus Grun. Denkschr. Akad. Wien 48: 79. L884. 



Willemoesia Castr. Rep. Voy. Chall. Bot. 2: I6b.pl. S.f. >. 8a, 8b. L886, no species. 

 Ethmodiscus Castr. Rep. Voy. Chall. Bot. 2: L66. pi. S. f. l. 9. L886. 



The above condensation results in a genus of huge proportions, the type of the 

 discoidal diatoms, as the genus Navicula is of the elongated forms. The general 

 structure of its valves is, as the name indicates, a circle covered with a hexagonal 

 network, a "sieve-disk. ' But the rather unwieldy dimensions of the genus is more 

 than offset by the definiteness of type which it affords. The differences upon which 

 the above synonyms were formed arc none of them confined to the Bpeciee that would 

 be therein included, but grade off into other forms thai are unmistakable examples 

 of Coscinodiscus. One example will Buffice, Cestodiscus Grev. Its generic char- 

 acter rests on the -mall submarginal processes that adorn the valves. But such proc- 



a little smaller, are the rule rather than the exception in < oscinodic 

 example in C. subtilis Ehrenb. Greville himself remark-: "I honestly confess that 

 the best generic character I can frame is weak." The Foregoing is equally applicable 

 to Beterostephania Ehrenb. The most unsatisfactory member of the above com- 

 bination to me is Endictya Ehrenb. The close resemblance of its members to the 

 evident Coscinodiscus forms C. robustu* Grev. and C. marginatum Ehrenb. is responsi- 

 ble for this union. But they are also close t" Borne specimens of Stephanopyxis, and 

 besides have certain peculiarities found in no other Coscinodiscus. The valv< 

 nol Hat or convex disks, but cups; not bounded by a ring-like margin, but when 

 viewed from the valval Bide, encircled by a somewhat raised and pointed edge from 



akschr. Akad. Wien 48-: 90. pi. 5., L884. 



