. The Geology of Minnesota . a. For further remarks on this genus see underTetradella. Ceratopsis chambersi Miller. PLATE XLVI. FIGS. 10-22. Beyrichia chambersi Miller, 1874. Cin. Quar. Jour. Sci., vol. i, p. chambersi Uluich. 1890. Jour. Cin. Soc. Nat. Hist., vol. xiii, p. 112. Size.—Length mm.; hight mm.; thickness mm.; hight mm. The principal distinguishing feature of this abundant species is the spine-likeform of the post-dorsal process. In the typical variety, of which fig. 19 is a fairexample, the post-medium ridge is short and small. It is

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. The Geology of Minnesota . a. For further remarks on this genus see underTetradella. Ceratopsis chambersi Miller. PLATE XLVI. FIGS. 10-22. Beyrichia chambersi Miller, 1874. Cin. Quar. Jour. Sci., vol. i, p. chambersi Uluich. 1890. Jour. Cin. Soc. Nat. Hist., vol. xiii, p. 112. Size.—Length mm.; hight mm.; thickness mm.; hight mm. The principal distinguishing feature of this abundant species is the spine-likeform of the post-dorsal process. In the typical variety, of which fig. 19 is a fairexample, the post-medium ridge is short and small. It is so in all the Trentonspecimens and in the Lower Cincinnati group types of the species. Figure 22 ispeculiar in having the upper end of this ridge separately developed as a smallrounded node. It is the only case of the kind seen, and may be abnormal. OSTRACODA. 677 Variety robusta, n. var. Beyrichia chanibersi Hall and Whitfield, Pal. Ohio, vol. ii, p. 104, pi. 4, flgs. 11, 12, not strictly B. chambersi

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