SYSTEMATIC CLASSIFICATION OF ECHINI. 227 



imperforate in the known species. They are typically all insert, or reaching the periproct, 

 but exceptionally one or more to all may be exsert (Plate 33, figs. 11, 12). Genitals have from 

 two to five pores each, and a madreporite is rarely recognizable (text-fig. 243, p. 331). The 

 periproct is plated with numerous thick plates (Plate 34, fig. 6), as in the Cidaroida, but these 

 plates are rarely preserved. The lantern is imperfectly known, but has the essential Palae- 

 ozoic characters as far as preserved. The spines in the whole family are essentially alike, small 

 secondaries on ambulacral and interambulacral areas; tubercles are imperforate and evenly 

 distributed over the corona (Plate 61, fig. 8). The existence of secondary spines and imper- 

 forate tubercles only may both be considered specialized characters. One species, Maccoya 

 phillipsiae, is said to be Silurian, but all others in the family are Lower Carboniferous (p. 302). 



The family characters are of course understood in the brief description of generic characters 

 given here. Palaeechinus M'Coy has only two columns of plates throughout each ambulacral 

 area, all plates are primaries of equal height, pore-pairs uniserial. Interambulacra with four 

 to six columns of plates in each area. The best known species are Palaeechinus quadriserialis 

 (Plate 29, fig. 1; Plate 30, figs. 1-7) and Palaeechinus elegans (text-fig. 237; Plate 29, figs. 

 3, 4, 6; Plate 31, figs. 1-5), (p. 304). 



The genus Maccoya Pomel differs from Palaeechinus in that at the mid-zone pore-pairs 

 are biserial. All ambulacral plates extend to the middle of the area, but marginally alternate 

 plates meet the interambulacrum, or are nearly or quite cut off from it by the outer enlargement 

 of their fellows {M. intermedia, Plate 34, fig. 2). This makes alternate plates primaries and 

 occluded instead of all primaries as in Palaeechinus. In some species the alternate plate may 

 weakly reach the interambulacrum instead of being cut off, M. sphaerica (Plate 34, fig. 5). 

 Such make an approach to the character of Palaeechinus, but, as the pore-pairs are biserial, 

 it seems best to consider them in this genus. On the interior of the test the plates all cross 

 the half-areas and pore-pairs are uniserial, a radical difference from the exterior of the same 

 structures (Plate 33, figs. 4, 5). The interambulacra have from four to nine columns of plates 

 in each area in the several species. A very perfect periproct is known in M. sphaerica. The 

 best known species are Maccoya burlingtonensis (Plate 32, figs. 1-3; Plate 33, figs. 1-5), M. 

 intermedia (Plate 33, figs. 6-12; Plate 34, figs. 1-3), and M. sphaerica (Plate 32, figs. 4, 5; 

 Plate 34, figs. 4-10), (p. 311). 



The genus Lovenechinus gen. nov. includes species in which at the mid-zone the ambula- 

 crum consists of four columns of plates. In each half-area there is a vertical series of demi- 

 plates which extend from the interambulacrum inward and a similar series of occluded plates 

 that extend from the middle of the ambulacrum outward, but neither series crosses the half- 

 area (Plate 42, fig. 2). Ventrally and dorsally the plates for a brief space are all primaries, 

 and, between these and the character plates, are plates which are alternately primaries and 

 occluded (Plate 42, figs. 1, 3 and 4; text-fig. 237). In this genus there are no isolated plates. 



