314 ROBERT TRACY JACKSON ON ECHINI. 



which is about the usual size in this family. The oculars and genitals are shown well in one 

 specimen in the Museum of Comparative Zoology (3,196). In this specimen, which is an 

 internal view, three oculars are in place, all are insert and adorally cover the ambulacra and 

 laterally the interambulacra in part on either side. One of the two genitals has three pores, 

 the second genital is obscure on this point. 



Upper Burlington Limestone, Lower Carboniferous, Burlington, Iowa, F. Springer Collec- 

 tion, eight specimens; Museum of Comparative Zoology Collection 3,011, 3,047-3,050 and 

 3,194-3,196; E. Kirk Collection. The holotype is said to be in the Worthen Collection, now 

 in the University of Illinois, at Urbana, Illinois. 



*Maccoya intermedia (Keeping). 

 Plate 33, figs. 6-12; Plate 34, figs. 1-3. 



Palaechinus (?) intermcdius Keeping, 1876, p. 37, Plate 3, figs. 9-11. 



Palaccchinus intermcdius Duncan, 1889, p. 203, text-figs, ix, x. 



Rhocchinus clegans (by error of identification) Jackson, 1896, text-fig. 1, pp. l9l, 205, Plate 7, fig. 10. 



Palechinus intermedium Tornquist, 1897, p. 739. 



Palaechinus intermcdius Klem, 1904, p. 33; Lambert and Thiery, 1910, p. 119. 



I have had the privilege of studying fine material of this species at Cambridge, England, 

 and at Munich, Dublin, and London. Test spheroidal. Ambulacra narrow, with two columns 

 of low plates, all of which meet the middle of the area. On the exterior of the test at the mid- 

 zone alternate plates are primaries, enlarged on the margin, and four of these primaries equal 

 the height of an adambulacral plate; the intermediate plates are narrowed marginally and' 

 cut off from interambulacral contact by the enlargement of their adjacent plates on either 

 side, and therefore are occluded. Pore-pairs are biserial, the outer pores of the occluded plates 

 falling in line with the inner pores of the primary plates (Plate 33, figs. 6, 7). As seen from 

 the interior all ambulacral plates cross the half-area completely and pore-pairs are uniscrial 

 (Plate 33, figs. 8, 9; Plate 34, fig. 3), (p. 60). 



In the interambulacra there are four columns of hexagonal median and pentagonal adradial 

 plates in each area, as ascertained in six specimens. Keeping was evidently mistaken in think- 

 ing that there might be five columns, and his doubt on the point is indicated by the fact that 

 he queried the statement. Developmental details of the interambulacra are not known, as all 

 specimens are wanting ventrally, but they are doubtless the same as shown in burlingtonensis. 

 Ambulacral and interambulacral plates bear numerous small secondary tubercles, but the spines 

 are unknown. Ambulacral plates bevel over the interambulacrals on the adradial sutures as 

 in all of this family, but the sides of the plates otherwise are as nearly parallel as is possible 

 in a curved test, and there is no imbrication. Keeping was certainly mistaken in saying that 



