OLIGOCENE ECHINODEBMATA. 173 



broad in petaloidal portion, narrow beyond; petals long, suboqual in length, almost closing. 

 Peristome rather large, pentagonal, transversely elongate, excentric anteriorly, more so than the 

 apical system, with a floscelle. Periproct rather large, elliptical, transverse, supramarginal, at 

 the top of a broad shallow groove and beneath an overhanging expansion of the test. 



Dimensions. — Length 69 millimeters; width 63 millimeters; height 29 millimeters. 



Description. — This large Cassidulus, the largest representative of the genus from American 

 Cenozoic deposits, is very rare, only a few specimens having been discovered. The test is 

 moderate to large in size, nioundlike in form, depressed, subquadrate in marginal outline; margin 

 thick, somewhat flattened on the sides, more angular at the ends, sharply angular beneath the 

 periproct. The upper surface is convex, and declines gently from the apex nearly equally on 

 all sides, though the side outlines tend to be straight while the end outlines tend to be curving; 

 a slight tumidity exists along the medial line above the periproct. The under surface is decidedly 

 concave along a broad, longitudinal median area. The apex is nearly central, being but slightly 

 excentric anteriorly. 



The ambulacral areas are narrow at the ambitus, dorsal portions petal oid; petals rather 

 wide, long, of nearly equal length, almost closing at their extremities. The poriferous zones are 

 rather wide, slightly depressed; pores subequal, outer row oval, inner row round; pairs of pores 

 conjugate; interporiferous areas slightly tumid. 



The surface of the test is closely set with small scrobiculate tubercles which increase in size 

 on the under surface except along a rather narrow median pitted area. 



The apical system is large and slightly excentric anteriorly, somewhat anterior to the apex. 

 There are four genital pores, the anterior pair being nearer together than the posterior, and there 

 are five minute pores perforating the radial plates. 



The peristome is rather large, pentagonal, transversely elongate, excentric anteriorly, more 

 so than the apical system, being about three-eighths the length of the test from the anterior 

 margin. It is surrounded by a large, well-defined floscelle, with prominent bourrelets. 



The periproct is rather large, elliptical, transverse, supramarginal, rather high up, at the 

 top of a broad shallow groove and beneath a rounded overhanging expansion of the test. 



Related forms. — Cassidulus alabamensis is closely related to C. gouldii, from which it is readily 

 separated by its greater size and its relatively low almost regularly convex upper surface. It 

 does not appear to be closely related to any foreign form. 



Localities. — Natural Bridge, St. Stephens, Ala. ; A. E. Belcher's well, Decatur County, Ga. 



Geologic horizon. — St. Stephens limestone (upper part), lower Oligocene. 



Collection.- — Johns Hopkins University (type). 



Genus ECHINOLAMPAS Gray. 



Echinolampas aldrichi Twitchell, n. sp. 



Plate LXXXI, figures la-d, 2. 



Determinative characters. — Test large, subcircular; margin rounded; upper surface depressed 

 subcorneal, sloping more steeply anteriorly than posteriorly; under surface concave, posterior 

 end slightly rostrate; apex forward of the center. Ambulacral areas rather narrow, dorsal por- 

 tions petaloid; petals long, open at the ends, poriferous zones of some petals unequal in length, 

 interporiferous areas tumid. Apical system excentric anteriorly. Peristome large, excentric 

 anteriorly, slightly less so than apical system, pentagonal, transversely elongate, surrounded by a 

 floscelle with feeble phyllodes and bourrelets. Periproct large, elliptical, transverse, infra- 

 marginal. 



Dimensions. — Specimen A (type, smaller than the average): Length 56 millimeters; width 

 54 millimeters; height 26 millimeters. Largest specimen: Length SO millimeters; width 75 

 millimeters; height 37 millimeters. 



Description. — Of this fine Echinolampas the only specimens so far reported belong to T. H. 

 Aldrich, of Birmingham, Ala., in whose honor the species is named. 1 The test is large (ranging 



t The Aldrich collection is now owned by the Johns Hopkins University. 

 39800°— 15 12 



