66 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



at about two-fifths of the circumference, which is the most charac- 

 teristic mark of this species, I do not know, not having access to 

 Smith's specimen; but his figure fails to show it; as do some other 

 of the earlier illustrations. Without these it is easily confused with 

 delicate specimens of C. centralis. Its color when dry has no distinc- 

 tive valve, yellow, buff, brown, and even blue-green valves being 

 present in the same slide. 



COSCINODISCUS DENTICULATUS Castracane 



(Castracane, Chall. Exp., pi. 3, fig. 8; Rattray, Rev. Cose, p. 83.) 



COSCINODISCUS EXCENTRICUS Ehrenberg 



(Ehrenberg, Mikrogeologie, pi. 18, fig. 32, pi. 21, fig. 6; Schmidt, Atlas, pi. 58; 

 figs. 46-49; Van Heurck, Synopsis, pi. 130, figs. 4, 7. 8.) 



COSCINODISCUS EXIGUUS Rattray 



(Schmidt, Atlas, pi. 58, fig. 30 (no name); Rattray, Rev. Cose, p. 130.) 

 This is another species peculiar to both Campeche Bay and the 

 Philippine Islands. 



COSCINODISCUS GAZELLAE Janisch 



(Grunow, Diat., Casp. Meere (Kittons's translation) in Journ. Roy. Micro. 

 Soc, 1879, pi. 21, fig. 8; Castracane, Chall. Exp., pi. 14, fig. 4 (no name); 

 Rattray, Rev. Cose, p. 98.) 



There is no adequate description and no good illustration of this 

 remarkable diatom. The figure in the Report of the Challenger 

 Expedition is a mere fragment of the valve and that in Kitton's 

 translation is indistinct. Nor is there much help to be obtained 

 from the "Eihmodiscus" figures in the Report of the Challenger 

 Expedition (pi. 14, fig. 3, 4a-4c (not 4), 5, 6; pi. 22, fig. 10) which 

 Rattray huddles together as synonyms of this species (see Rattray, 

 Rev. Cose, p. 98) . The diatom is almost impossible to find unbroken, 

 though it is abundant in the Philippine Islands, because of its enor- 

 mous size and its extremely fragile character. Its most striking 

 mark of distinction is the many short wavy lines running transversely 

 across the delicate radiating beading of the valve, this cross-hatching 

 becoming more abundant toward the the margin. This is well shown 

 in the unnamed fragment in the above-mentioned Report of the 

 Challenger Expedition (pi. 14, fig. 4; not 4a-4c). By this it may be 

 easily distinguished from the somewhat smaller C. rex Wallich, as well 

 as by the absence of the cluster of papillae in the central area of the 

 latter. 



COSCINODISCUS HETEROMORPHUS Rattray 



(Schmidt, Atlas, pi. 65, fig. 17 (no name); Rattray, Rev. Cose, p. 468 (p. 20).) 



It bears considerable resemblance to C.spendidus Greville as shown 



in the Microscopical Journal for 1865, plate 5, figure 3, but not to the 



