MELONECHINUS. 373 



it is from Middle Tennessee, and he had reason to think from the Lithostrotion bed which 

 belongs to the St. Louis Group of the Lower Carboniferous. The holotype is in Vanderbilt 

 University Collection, Nashville, Tennessee, 223. Casts of this specimen are in F. Braun's 

 collection; and in the Museum of Comparative Zoology Collection 3,150. 



*Melonechinus septenarius (Jackson). 



Plate 51, fig. 10; Plate 53, fig. 5. 



Melonites septenarius Jackson, 1896, p. 182, Plate 9, fig. 49; Klem, 1904, p. 43. 

 Mdoncchinus septenarius Lambert and Thiery, 1910, p. 121. 



The test is small and spheroidal. The type and only known specimen is an internal sili- 

 ceous mold, so that the external characters, including melon-like ribs, are unknown. Width 

 of the ambulacrum at the mid-zone about 13 mm., width of the interambulacrum 23 mm. 



The ambulacrum at the mid-zone has eight columns of plates. As the plates are internal 

 impressions, the pore-pairs are near the outer border of occluded plates, the inner border of 

 demi-plates, and about the middle of isolated plates (compare Plate 56, fig. 5). About three 

 demi-plates equal the height of an adradial plate. There are seven columns of interambulacral 

 plates in an area. The seventh column is peculiar in that it originates far to the right of the 

 center, but has as usual a heptagonal plate on its left ventral border. Near the mid-zone an 

 adventitious pentagon, P, occurs, and next to it on the right is a heptagon, A, the extra side 

 of which compensates for the missing side of the pentagon. 



This species is imperfectly known. It is structurally nearest to M. indianensis, but differs 

 in that the ambulacra are proportionately much wider and the seventh column, which is ex- 

 ceptional and late in development in indianensis, appears very early in septenarius. 



Warsaw Limestone, Lower Carboniferous, Buzzard's Roost, Franklin County, Alabama. 

 Holotype in the American Museum of Natural History Collection ^ . 



*Melonechinus obovatus sp. nov. 

 Plate 53, figs. 9, 10; Plate 54, figs. 2, 3. 



This species is a remarkable type in its character, but is only known from one specimen, 

 which is an internal yellowish calcite mold, so that external characters, including the melon- 

 like ribs, are unknown. Test slightly higher than wide, obovate, and apparently in its original 

 shape without distortion. As the specimen is an internal mold, its horizontal outline presents 

 a continuous curve of one arc (Plate 54, fig. 3), there being no indication of the melon-like ribs 

 which doubtless existed on the exterior. As these ribs are formed mainly by the thickening 

 of the plates, their outline is usually not indicated on the interior of the test (compare Plate 

 38, fig. 9; pp. 359, 371). Height about 43 mm., diameter through the ambitus 42 mm.; this 

 measurement exceeds the diameter through the mid-zone, as this is one of the very rare cases 

 in which the ambitus, or greatest circumference, is dorsal to the middle of the test (p. 32). 



