246 CONTRIBUTIONS FROM TllK NATIONAL HKRHAHIUM. 



ppacew between, the bosses or l>ea(ls; below tliis donble-inarkod outer plate n second 

 plate regularly dotted (or perforated?), the dotting appearing thron<Th the bosses and 

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

 of juncture of the two \ alvea, hyaline (not seen in the acconipanj'ing figure, bi*ing 

 out of focus). 



Diameter of valve, 0.078 mm. 



I confess to some doubt in referring my form to this genus; though its resemblance 

 makes me ])refer to classify it here rather than accept the less advisable alternative 

 of creating a new genus for it. The correctness of placing it here is rendered more 

 probable by its near resemblance to Stcphanopyris broschti Grun..'^ especially the last 

 fi.G:ure, My species differs from that of Gruncju in everything except the secondary 

 punctatiou; in the large number of knob-Iikc processes, toward the margin filling 

 all the interspaces, in the evident hyaline border, in the absence of "two to five 

 spines remote from the center." Of (Jrunow's figure which most nearly resenibles 

 this species, namely, figure 30, he says: ^* P^ig. 30. Form ohne Stacheln, fragli<.'h hieher 

 gehorend." 



Type in theU. S. National Museum, No. 500119, from station 2807, (ialapagos Islands, 

 April 1, 1888; 8 12 fathoms, botti^ni of ( luliigerina ooze and coral jnud. 



COSCINODISCUS Ehrenb. 



Cosdnodlscus Ehrenl). Phys. Abb, Akad. Wiss. Berl. 1838: 128. 1840. "Ratt. 



Proc. Roy. Soc, Edinb. 16: 449. iS89. De Toni, Syll. Alg. 2: 1200. 1894, 

 Sy mholoplf or a YAvcQwh, in part; Ber. Akad. Wiss. Berl. 1844: 205. 1845. 

 Endictya Ehrenb. Ber. Akad. Wiss. l^-erl. 1845: 71. 1846? 

 Odoniodisctfs Ehrenb. Ber. Akad. Wiss, Berl. 1845: 72. 184C. 

 IleUrodcphania Ehrenb. Mikrog. 15. pi, S5A. XIII^ B,f. 4, 5, 1854, 

 Cestodiscus Grev. Trans. Micr. See. Loud, n. s. 13: 48. pi. 5.f. cS\ 9. 18G5. 

 Cosviiodiscus Grev. Trans. Micr. Soc. Lend, n, s. 14; 79, pi. S.f, 11-13. 18GG. 

 Stoschla Jan.] Van Ileur. Synop. pi, 12S,f. 6. note. 1881. 

 Janischia Grun.; Van ITeur. Synop. pi. 95./. iO-lU 188L 

 MicropodiscHS Grun. Benkschr. Akad. ^^'ien 48: 79. 1884. 



WillfvmmaQ'A^Xr, Rep. \o\\ Chall. Bot. 2: W^. pi. S.f. S\ 8a, Sh. 1886, nn spetaes. 

 Elhmodis^ctis Castr. Bep. \'oy. (^hall. P>ot. 2: 106. pL S.f. i, 9, 1886. 



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

 disc(udal <liatoms, as the genus Navicnla is of the elongated forms. The general 

 structure of its valves is, aa the name indicates, a ( ircle c<»\ered with a hexagonal 

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

 than offset by the definiteness of type whioli it affords. The (tiflerences upon which 

 the above synonyms were formed are none of them confmed to the species that woulfl 

 be therein included, but grade off into other forms that are umnistakable exantples 

 of Goscinodiscus. One example will suflice, Cestodiscus Grev. Its generic ohar- 

 acter rests on the small submargimd ]>ro('esses that adorn the valves. But such proc- 

 essesj a little smaller, arc the rule rather than the exception in t oscinodiscus, as for 

 example in (', suhtiUs Ehrenb. Grcville himself remarks: *'l honestly confess tliat 

 the best generic character I can frame is weak.'' The foregoing is equally applicable 

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

 bination to me is EndicL^a Ehrenb. The close resemblance of its members to the 

 evident Coscinodiscus f(^rins C, rohuHluH CJrev. an<l C. warginaias Ehrenb. is respojisi- 

 ble for this union. But they are also close to some specimens of Stephanojiyxis, and 

 besitles have certain peculiarities found in no other Coscinodiscus. The valves aro 

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

 viewed from the valval sitle, encircled l)y a somewhat raised and pointed edge from 



f'Denkschr. Akad, Wien 48-': 90. pi. f>.f. ^6-30. 1884. 



