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4 50 
times only one present, robust and spine-like, with blunt extremities 
inserted at or near inner edge of border, more rarely at some 
distance from it ; a small hyaline space sometimes present around 
the base of each. Border narrow or broad, hyaline or striated, the 
striae sometimes faint. — Symbolophora , Ehrb., pro parte, Mon. Ber. 
Ak., 1844, p. 74 ; Endidya , Ehrb., ibid ., 1845, p. 71 ; Odontodiscus , 
Ehrb., pro parte, ibid., 1845, p. 72; Heterostephania, Ehrb., Microg. 
(plates), p. 15; Cestodiscus , Grev., Trans. Micr. Soc. Bond., 1865, 
p. 48; Cosmiodiscus , Grev., ibid., 1866, p. 79; Stoschia, Janisch., 
van Heurck, Syn. Diat. Belg., Explan. pi. cxxviii. fig. 6 ; Janischia ? 
Grun., Yan Heurck, ibid., Explan. pi. xcv. bis figs. 10, 11 ; Micropo- 
discus, Grun., Denk. Wien. Ak., 1884, p. 79; Willemoesia, Cstr., 
Diat. Ghall. Exped., 1886, p. 165; Ethmodiscus, Cstr., ibid., p. 166. 
§ I. Inordinati. 
Round or elongately elliptical. No rosette ; a central space rarely 
present, sometimes excentric. Markings punctiform, granular or 
areolate, without order. 
C. exasperans, sp. n. Sch., Ail., pi. lviii. fig. 9 (no name). — 
Diam. about *018 mm. Central space and rosette absent. Markings 
small, round., granular, slightly smaller near the border ; interspaces 
hyaline, largest towards the centre ; non-apiculate. Border sharply 
defined, hyaline. 
Habitat. — Monterey (Schmidt). 
C. dimorphus , Cstr., Diat. Chall. Exped., p. 157, pi. xvii. fig. 6. 
— Diam. *0225 mm. Central space absent. Markings punctiform, 
irregular, sometimes most crowded towards the centre, and few on 
a narrow band around the border or conversely, those of the two 
valves of a frustule dissimilarly arranged. Border sometimes 
distinct. — Sch., Atl., pi. lvii. fig. 1 (no name). 
Distinguished from C. marginidatus by the smaller number of 
markings and the absence of apiculi. Some valves approach the 
minute Cyclotella pumila, Cleve (Yan Heurck, Syn. Diat. Belg., 
pi. xciv. fig. 16). 
Habitat. — South Atlantic, H.M.S. Challenger (Castracane) ; 
Sandwich Islands (Schmidt). 
