344 ROBERT TRACY JACKSON ON ECHINI. 



relatively smaller than in the young individual (p. 342). Oculars are insert, ventrally cover the 

 ambulacra, and laterally the interambulacra in part on either side. Two of the oculars show 

 pores ventrally as indicated by siliceous plugs like those previously described. The genitals 

 are high, wide, with three or four pores each. These are represented by delicate siliceous 

 tubes which were evidently formed as post-mortem linings to the original pores and before 

 the solution of the plates. A few molds of periproctal plates are in place (Plate 42, fig. 6) ; they 

 are small, angular, as in other species in the family, and are the only ones yet known in this 

 genus. Impressions of jaws are imperfectly seen ventrally (Plate 39, fig. 4). 



A specimen that I gave the British Museum, now no. E 10,679 of its collection, is a large 

 individual measuring 83 mm. in diameter. It is a dark brown, silicified internal mold from 

 near Webb City, Missouri. The ambulacral plates are demi- and occluded at the mid-zone, 

 but primaries only close to the oculars. In three interambulacral areas. A, C, and G, there are 

 six columns of plates. In each the sixth column is represented by a considerable number of 

 plates, more than in any other specimen of the species seen. The exact number could not be 

 ascertained as the point of origin of this column is not preserved in any area, but in area G 

 a sixth column is represented by at least ten plates, above which it drops out, and there are five 

 columns; and far dorsally, another column drops out, so that only four columns are in contact 

 with the apical disc, as in area E of Plate 41, fig. 3. Dorsally molds of the five oculars are 

 in place, all are insert, and ventrally cover the ambulacra and laterally the interambulacra in 

 part on either side. The genitals are high, wide, with several pores each, but details of the 

 pores are imperfect. 



A specimen from Coriscana, Missouri, in the Yale University Museum Collection, is well 

 preserved and is practically spherical (Plate 44, fig. 2), measuring 59 mm. in height, 62 mm. in 

 diameter through the mid-zone in the view shown, and also 59 mm. in diameter in the same 

 plane, but at right angles to that figured. The specimen is an internal siliceous mold and shows 

 the impression of plates clearly. There are five columns of plates in each interambulacral 

 area at the mid-zone, and in no area is a sixth column developed. The oculars are all in place 

 and insert; genitals are high, wide, with three pores in two of the plates, five pores in two, and 

 in one genital the pores are indistinct. Another specimen from Coriscana in the Yale Collec- 

 tion, no. 313, is very large and somewhat elongated by compression. It measures 114 mm. in 

 height, 101 mm. in diameter through the mid-zone in one plane, and 76 mm. in diameter through 

 a plane at right angles to the same. There are five columns of plates in all the interambulacral 

 areas, though one area is obscure at the mid-zone. The genitals are high, wide, two with three 

 genital pores, two with four, and one with five pores. 



A choice specimen from Webb City, Missouri, in the Museum of Comparative Zoology 

 Collection, no. 3,125, has on one side a siliceous mold of the interior and on the other a siliceous 

 mold of the exterior, the spaces originally occupied by the plates being hollow (Plate 44, figs. 3, 



