120 MESOZOIC AND CENOZOIC ECHINODEKMATA OP THE UNITED STATES. 



The surface of the test is covered with numerous small but rather conspicuous tubercles set 

 in relatively large scrobicules. 



The peristome is central, relatively large, circular. The periproct is small, about one-half 

 the diameter of the peristome, situated near the margin, being about one-fourth of the distance 

 from the margin to the peristome. 



Related forms. — E. Tiuxleyanus is closely related to E. parvus. In fact, it is quite possible 

 that with the discovery of some good specimens of Emmons's form E. Tiuxleyanus may be found 

 to be identical and be reduced to a synonym. It appears to differ from E. parvus, however, in 

 having its periproct nearer the margin and in being more pointed anteriorly. It also resembles 

 both E. texanus and E. vaugliani, but differs from them in having thinner walls, in being less 

 elevated, and in not having its periproct near the peristome. 



Locality. — Claiborne, Ala. 



Geologic horizon. — Gosport sand, Claiborne group, middle Eocene. 



Collections. — U. S. National Museum (figured form); Johns Hopkins University (T 2006). 



Echinocyamtjs texanus Twitchell, n. sp. 



Plate LVII, figures 2a-d. 



Determinative characters. — Test very small, ellipsoidal, oval in marginal outline. Upper 

 surface elevated, somewhat flattened in the center; lower surface flattened around the nearly 

 flush peristome. Apical system with four medium-sized genital pores; madreporite tumid. 

 Petals long, the anterior three nearly reaching the margin, wide open at ends. Peristome 

 relatively large, central; periproct very small, close to peristome. 



Dimensions. — Length 5 millimeters; width 4 millimeters; height 2.5 millimeters. 



Description. — Only a single specimen of this new Echinocyamus has been discovered. It 

 was found by Mr. T. EL Aldrich of Birmingham, Ala., who reports that it was found in the 

 "Lower Claiborne" deposits of Lee County, Tex. The test is thick-walled, very small (it being 

 one of the smallest of American echinoderms), regularly oval in marginal outline, and ellipsoidal 

 in general form. The upper surface is elevated, somewhat flattened centrally; the lower sur- 

 face flattened near the nearly flush peristome and the periproct. 



The ambulacral petals are rather well defined, relatively long, all of about equal length, 

 the anterior three extending nearly to the margin as seen from above. The poriferous zones 

 diverge in almost straight lines to the ends where they are wide apart; they consist of small 

 round pores in pairs which are apparently not conjugated. 



The apical system is subcentral or very slightly excentric anteriorly, coincident with the 

 apex, with four moderate-sized genital pores set near together, the anterior pair but slightly 

 nearer together than the posterior pair. A small, swollen, button-shaped madreporite just 

 reaches to the genital pores. 



The peristome is relatively large, central, nearly flush with the lower surface; periproct 

 very small, about one-third of the diameter of the peristome, and is situated at a distance from 

 the peristome equal to its own diameter. 



Belated forms. — E. texanus is most closely related to E. vaugliani, but is easily distinguished 

 from it by its less egg-shaped form, smaller size, less pointed anterior end, and less difference 

 between its longitudinal and transverse diameters. E. texanus also resembles E. parvus and 

 E. huxleyanus but differs from both in having its periproct near the peristome. It also differs 

 from E. Tiuxleyanus in being less fragile, less depressed, and less pointed anteriorly. 



Locality. — Lee County, Tex. 



Geologic horizon. — Lower part of Claiborne group, middle Eocene. 



Collection. — Johns Hopkins University (T 2002). 



