352 ROBERT TRACY JACKSON OX ECHINI. 



Interambulacra broad, elevated in a moderate curve from the adradial sutures, with six 

 or seven columns of plates in each area. In one specimen (Plate 48, fig. 1) one area, A, as an 

 exception is very narrow, and has four columns of interambulacral plates, but the next ad- 

 jacent area, C, has seven columns. This specimen, on account of the four colunms in one area, 

 was considered a distinct species by Miller and Gurley, and described as Oligoporus bellulus. 

 The ventral and dorsal portions are unknown. Ambulacral and interambulacral plates bear 

 small secondary tubercles, and one specimen has numerous small tapering spines about 2.5 mm. 

 in length. 



The specimen which Miller and Gurley described as the type of Oligoporus bellulus (Plate 

 47, fig. 6; Plate 48, fig. 1) I feel is nothing more than a very peculiar exception. The ambula- 

 crum and interambulacrum C with seven columns are quite normal for the species. The 

 interambulacrum A is certainly very exceptional in having only four colunms; no such range 

 in two areas of one individual has been seen in any other specimen in this family. It may, 

 however, better be considered an extreme arrested variant in this one area rather than as a 

 basis for a distinct species. I therefore consider bellulus a synonym of blairi. Miller and 

 Gurley do not mention that there are seven columns in one of the areas of this specimen. It 

 has numerous small spines as described above. 



One of Miller and Gurley's cotypes of blairi (Plate 47, fig. 7; Plate 49, fig. 1) represents a 

 considerable part of the dorsal half of a test. It is perhaps the most characteristic of all the 

 specimens. The interambulacra A and C have each seven columns of plates. Miller and 

 Gurley give six columns as the species character, but do not mention a seventh. I do not quite 

 understand how they overlooked this feature. This specimen shows the surface form of the 

 areas better than any other. 



A second cotype (Plate 49, fig. 3) represents about the middle of the corona. In area A 

 there are six columns of plates; ventrally the initial pentagonal plate of column five is seen in 

 the middle line and in the second row from the base. The initial pentagon of column six is 

 seen in the sixth row from the base, and a heptagonal plate lies on its right ventral border. 

 In area C there are six columns of plates and indications of a seventh column as shown by the 

 pentagon, with a heptagonal plate on its right ventral border lying 30 nun. from the base of 

 the specimen and with three columns of interambulacral plates lying between this pentagon 

 and ambulacrum D. 



The third cotype of blairi and the smallest specimen (Plate 49, fig. 2) has six columns of 

 interambulacral plates in area A. The initial plate of the sixth column is a pentagon with a 

 heptagon on its left ventral border and lying just below the middle of the area. In area C 

 there are seven columns of interambulacral plates. The initial plate of column 5 lies 7 mm. 

 above the ventral border of the specimen, and there is a heptagonal plate on its right ventral 

 border. Three rows above appears the initial pentagon of column 6, with a heptagon on its 



