324 ROBERT TRACY JACKSON ON ECHINI. 



In the Kentucky specimen referred to this species (Plate 34, fig. 12) there are seven columns 

 of interambulacral plates at the mid-zone in each area, but an eighth column originates dorsally 

 in each area, and in area C a ninth column is represented by a few plates near the apical disc. 

 The ventral portion is unknown in the species and the dorsal portion is unknown in the type, 

 but in this specimen, which is an external sandstone mold, impressions of insert oculars 

 and wide, high genitals are visible dorsally (Plate 35, fig. 3). 



Upper Burlington Limestone, Lower Carboniferous, Burlington, Iowa, holotype, from 

 the Wachsmuth Collection 407, in the Museum of Comparative Zoology Collection 3,052; 

 Lower Burlington Limestone, same locality and Museum 3,009; Waverly Group, Lower Car- 

 boniferous, Menifee County, Kentucky, two specimens on one slab. Museum of Comparative 

 Zoology Collection 3,062. 



The specimens from Menifee County, Kentucky (Plate 34, fig. 12; Plate 35, figs. 2, 3) 

 are the only ones of this species known excepting those from Burlington as described above. 

 The better of the two is figured. The specimen is an external sandstone mold of the dorsal 

 side, therefore in the figures the orientation is reversed from what it would be if viewed from 

 the exterior. The ambulacra are narrow, 5 mm. in width at the widest part, which is narrower 

 than in the type, but the specimen is smaller, and the interambulacra at the widest part are 14 

 mm. across. Details of ambulacral plates cannot be ascertained, and as restored by dotted 

 lines in Plate 34, fig. 12, are doubtless given incorrectly, but this figure was drawn in 1895 when 

 I had not studied the type. Interambulacrum A (Plate 34, fig. 12) is the most nearly com- 

 plete area; ventrally there are five columns of plates, above which the sixth and seventh col- 

 umns are introduced with pentagonal plates; farther dorsally, an eighth column comes in at 

 the left of the center with a heptagonal plate on its right ventral border (just the reverse as 

 seen from the exterior). In the several other areas there are seven columns of plates in the 

 most adoral portion preserved, and farther dorsally in each area, an eighth column is introduced 

 with a pentagonal plate. In area C the eighth column appears somewhat earlier than in the 

 other areas, and near the apical disc a ninth column is represented by three small plates. 

 This specimen occurs in the Waverly Group, which is somewhat older than the Burlington 

 Limestone, but I think the specimen is referable to M. gracilis. The only difi'erences seen 

 are the somewhat narrower ambulacra and the eighth column of interambulacral plates dor- 

 sally. The type might have shown this additional column if it were complete to the apical disc. 



LovENECHiNUS gen. nov. 



Test spheroidal, ambulacra relatively narrow, with four columns of plates at the mid- 

 zone, which consist of two columns of narrow demi-plates and two columns of wider occluded 

 plates, without intercalated isolated plates. The wide occluded plates are roundly arched 

 upward in the center, and this is the beginning of that dominating prominence of the two 



