EOCENE ECHINODEKMATA. . 121 



Genus SISMONDIA Desor. 

 Sismondia (?) plana Conrad. 

 Plate LVII, figures 4a-d. 



Sismondia plana Conrad, 1865, Acad. Nat. Sci. Philadelphia Proc, p. 75. 



Ifortonia (Periarchus) plana Conrad, 1S66, Smithsonian Misc. Coll., vol. 7 (200), p. 21. 

 Sismondia plana Cotteau, 1S91, Paleontologie francaise, Echinides eocenes, vol. 2, p. 299. 



Monostychia plana Gregory, 1891, Geol. Soc. America Bull., vol. 3, p. 108. 

 Periarchus (?) plana Stefanini, 1911,. Soc. geol. italiana Boll., vol. 30, p. 699. 



Determinative characters. — Test very small, very thin, subovate to subcircular in marginal 

 outline, rounded to somewhat pointed anteriorly and posteriorly. Upper surface very low, 

 slightly tumid centrally; apex and apical system more or less anteriorly excentric; lower sur- 

 face flat; margin very thin. Ambulacral petals subelliptieal, extending halfway to margin, 

 nearly closing at ends. Peristome slightly excentric anteriorly, small, circular; ambulacral 

 grooves well defined and simple halfway to the margin, then obscure but apparently not branch- 

 ing. Periproct very small, elliptical, about two-fifths the way from margin to peristome. 



Dimensions. — Length 17 millimeters; width 15 miUimeters; height 2 millimeters. 



Description. — The test of this species is very small, rarely exceeding one-half an inch in 

 diameter, very thin throughout, subovate to subcircular in marginal outline, rounded to some- 

 what pointed anteriorly and posteriorly, broadest back of the middle. The upper surface is 

 very low, slightly tumid centrally; the apex usually excentric anteriorly, sometimes subcentral; 

 the lower surface flat; the margin very thin. 



The ambulacral petals are well defined but small, extending only halfway to the margin, 

 broadly lanceolate to subelliptieal in outline, nearly closing at the ends ; several pairs of pores 

 extend beyond the ends of the petals. The poriferous zones are relatively narrow, inner row 

 of pores round, outer row oval, pairs of pores conjugated ; interporif erous areas rather narrow, 

 not much wider than the poriferous zones. 



The apical system is subcentral or excentric anteriorly, coincident with the apex. The 

 details could not be clearly made out on the specimens. 



The tuberculation is inconspicuous, the whole test being covered with small tubercles, in 

 shallow scrobicules, set closely together. 



The peristome is subcentral or slightly excentric anteriorly, small, circular. The ambula- 

 cral grooves extend as well defined simple fines from the jDeristome halfway to the margin, beyond 

 which point they become obscure; but do not appear to branch. 



The periproct is very small, elliptical, the longest diameter being longitudinal, located about 

 two-fifths of the way from the margin to the peristome. 



Related forms. — Scutella (?) conradi is closely related to Sismondia ( ?) plana but differs from 

 it in having its posterior border truncated and notched at the middle and opposite the posterior 

 petals, and its periproct nearer the posterior border. 



Locality. — The type came from South Carolina. (No more definite locality can be given.) 

 Some specimens came from near Charleston, S. C. 



Geologic horizon. — Eocene. 



Collection. — Academy of Natural Sciences of Philadelphia (10S0). 



Genus FIBTJLARIA Lamarck. 

 Fibularia meridionalis (Meyer). 



Plate LVII, figures 3a-d. 



Echinocyamus meridionalis Meyer, 1887, Fauna Alttertiiirs Mississippi und Alabama, p. 12, PL II, figs. 21, 21a. 

 Echinocyamus meridionalis De Gregorio, 1890, Mon. faune eocenique Alabama, p. 251, PL XLIII, fig. 14. 

 Echinocyamus meridionalis Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 697. 



Determinative characters. — Test thin walled and fragile, very small, discoidal, broadly oval 

 to subcircular in marginal outline. Upper surface very low, flat or nearly so; sides rounded; 

 lower surface slightly concave. Apical system central or subcentral; petals rudimentary, 



