174 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



from 2 to 3 inches in diameter) and about half as high as broad. The marginal outline is broadly 

 oval to subcircular; sometimes, especially in the larger and older forms, slightly broader pos- 

 teriorly than anteriorly and broadly V-shaped at the posterior end; margin tumid and rounded. 

 The upper surface is depressed subconical, though at times approaching a depressed subhemi- 

 spherical contour, sloping more steeply anteriorly and on the sides than posteriorly; under sur- 

 face concave, though slightly tumid around the margin except along the posterior ambulacral 

 areas where there are broad and very shallow depressions which give the posterior end of the 

 test a slightly rostrate appearance. The apex is forward of the center, about two-fifths of the 

 length of the test from the anterior end, coincident with the apical system. 



The ambulacral areas are rather narrow, dorsal portions petal oid; petals long, rather narrow, 

 open at their extremities, the posterior pair slightly longer than the anterior pair which are 

 slightly longer than the odd petal; interporiferous areas tumid. The poriferous zones are 

 rather narrow, slightly depressed, the inner zone of each of the posterior petals and the anterior 

 zone of each of the anterior paired petals being slightly straighter and shorter than its fellow, 

 the differences being the more pronounced in the anterior pair; outer pores slitlike, inner pores 

 round, pairs of pores conjugate. 



The whole surface of the test is closely set with very small, uniform tubercles in sunken 

 scrobicules. 



The apical system is excentric anteriorly. There are four perforated basal plates, the 

 anterior pair of genital pores being nearer together than the posterior, and five small perforated 

 radial plates. The madreporite is large, occupying the larger part of the system, and extending 

 back between the posterior radial plates. 



The peristome is rather large, excentric anteriorly, slightly less so than the apical system, 

 pentagonal, transversely elongate, at the deepest portion of the concave under surface, and 

 surrounded by a floscelle with feeble, straight phyllodes and low, broad, tumid bourrelets. 



The periproct is rather large, elliptical, the posterior side slightly less convex than the 

 anterior, transverse, inframarginal, very close to the posterior margin. 



Related forms. — Echinolampas aldrichi is quite unlike Echinolampas appendiculatus, the 

 only other representative of the genus found in the Cenozoic deposits of the United States. Of 

 foreign forms it is very similar to Echinolampas affinis (Goldfuss) Agassiz, which occurs in the 

 Eocene of Belgium and France, but it is to be distinguished by its more anteriorly excentric 

 apex and the somewhat unequally excentric positions of its apical system and peristome. It 

 also resembles Echinolampas insignis Duncan and Sladen from the Nummulitic series of the 

 Tertiary of India, from which, however, it differs in being smaller, less elevated, and having its 

 apex more excentric anteriorly. 



Localities. — Gainestown, and Choctaw Bluff, Alabama River, Alabama; Mississippi (exact 

 locality unknown). 



Geologic horizon.— St. Stephens limestone, Alabama; Vicksburg limestone, Mississippi; 

 lower Oligocene. 



Collection. — -Johns Hopkins University (T 1099, A). 



Suborder STERNATA. 



Family SPATANGID.E. 



Genus AGASSIZIA Valentin. 



Agassizia conradi (Bouve). 



Plate LXXXI, figures 3a-d. 



Hemiaster conradi Bouve, 1851, Boston Soc. Nat. Hist. Proc, vol. 4, p. 3, figures in text. 



Hemiaster conradi Desor, 1858, Synopsis echinodermes i'ossiles, p. 373. 



Hemiaster conradi Conrad, 1865, Acad. Nat. Sci. Philadelphia Proc, p. 75. 



Hemiaster conradi Conrad, 1866, Check list, Eocene and Oligocene. 



Ditremaster conradi Cotteau, 1887, Paleontologie francaise, Echinides eocenes, vol. 1, p. 427. 



Agassizia fioridana Be Loriol, 1887, Recueil zool. Suisse, vol. 4, pp. 398^101, PI. XVII, fig. 9. 



Opissaster conradi Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 700. 



Agassizia fioridana Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 705. 



