North American index fossils, invertebrates . to depth of five fathoms off coast ofSouth Carolina to the Bahamas, Cuba and Guadaloupe. (Thereseems to be no important difference between the Tertiary andRecent forms.) ECHINODERMA TA—ECHINOIDEA. 591 XVIIL Periarchus , with central apex more or less abruptly elevated,short ambulacra open at the ends, and extending only half way tothe margin; periproct on under side nearer the mouth than themargin. Eocenic-Oligocenic. 2y. P. lyelli (Conrad). Eocenic-Oligocenic. Margin thin, gently concave for less than one fourth the diam-eter, ris
North American index fossils, invertebrates . to depth of five fathoms off coast ofSouth Carolina to the Bahamas, Cuba and Guadaloupe. (Thereseems to be no important difference between the Tertiary andRecent forms.) ECHINODERMA TA—ECHINOIDEA. 591 XVIIL Periarchus , with central apex more or less abruptly elevated,short ambulacra open at the ends, and extending only half way tothe margin; periproct on under side nearer the mouth than themargin. Eocenic-Oligocenic. 2y. P. lyelli (Conrad). Eocenic-Oligocenic. Margin thin, gently concave for less than one fourth the diam-eter, rising abruptly in center to apical system; ambulacra uniform;length a little more than one fourth the diameter of test, actinalsurface flat; grooves bifurcating; diameter 80 mm. Claibornian of Alabama; Vicksburgian of Georgia. XIX. ScuTELLA very flat, subcircular in outline, sometimes undulating ornotched, broadest behind. Ambulacral furrows branching; petaloidpart of ambulacra unequal, well-developed, nearly closed; peri- /?. Fig, 1923. Scutella albeiti^ upper, lateral and lower view, X Yi- (Md. Survey.) stome small, central, subcircular; periproct very small, mostlyinframarginal; apical system central, more or less pentagonal. Tertiary. 28. S. alberti Conrad. (Fig. 1923.) , orbicular, very much depressed, but swelling towards the middle, and depressed at apex; diameter 160 mm. X (Choptank) of Maryland. (Abundant.) 29. S. fairbanksi Merriam. than preceding (maximum diameter 36 mm.), broadest posteriorly; margin scarcely notched. Lower Miocenic (Vaqueros formation) of California. 592 NORTH AMERICAN INDEX FOSSILS. XX. EcHiNARACHNius from Scufella in its excentric apical system. Pliocenic-Recent. 30. E. gibbsi Remond. outline much like Scutella fairhanksi, but larger, and apical system about one fourth the longitudinal diameter from the pos-terior end; ambulacra broad, the transverse gro
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