MEEKECHINUS. 443 



ambulacral and interambulacral plates. The peristome and ventral part of the test is frag- 

 mentarily known. Oculars are small, imperforate, covering the ambulacra and laterally in 

 part the interambulacra on either side. Genitals are large, with from two to five genital 

 pores. A well developed madreporite exists in the known specimens. The lantern is inclined, 

 of the usual Palaeozoic character, but the teeth on the outer face are vertically ridged and 

 distally deeply serrate, a unique character. 



This genus structurally differs from Pholidocidaris in that the dorsal interambulacral plates 

 are uniform in size and character instead of very dissimilar; it differs from all known genera in 

 the serrate teeth. I name this genus for the late Fielding Bradford Meek in recognition of 

 his critical and very accurate work on Palaeozoic Echini. 



The type and only known species is Meekechinus elegans sp. nov. from the Permian of 

 Kansas. 



'Meekechinus elegans sp. nov. 

 Plate 75, figs. 6-8; Plate 76, figs. 1-9. 



This species is known from three excellent specimens that were kindly sent me for study 

 by Professor J. W. Beede of Indiana University. The specimens consist of two very wonder- 

 fully preserved tests, seen in dorsal view, which are very nearly perfect from the apical disc to 

 the ambitus, and a third fragmentary specimen with ventral plates and a fine lantern. 



The test is spheroidal or flattened, probably the latter, as the tests are now quite flat and 

 without any obvious displacement of plates, and quite circular in outline, as seen from above. 

 Both specimens are very nearly alike in size and preservation, but that selected as the holotype 

 (Plate 75, fig. 6; Plate 76, fig. 1) measures 54 mm. in diameter through the axis III, 5. From 

 the center of the apical disc to the periphery of the test it measures almost exactly 27 nun. 

 radially in every direction, attesting to the absence of any distortion. At the periphery, which 

 I take to be the ambitus, the ambulacra measure 26 mm. in width in a straight line, or about 

 32 mm. in width following the curve of the periphery. The interambulacra measure 6 mm. 

 in width, and are strikingly uniform in their constant width from the ambitus to the apical disc. 

 In this respect they surpass any sea-urchin known to me. As seen from the measurements, 

 the ambulacra, measured on the curve of the periphery, are about five times the width of the 

 interambulacra, certainly an extraordinary development for the group, and in all Echini sur- 

 passed in this character only by Lepidesthes extremis, which proportionately has slightly wider 

 ambulacra, as described on page 430. 



The ambulacra are very wide, and at the ambitus, which is also doubtless the mid-zone, 

 there are twenty columns of plates in an area. Sixteen columns is the highest number known 

 in any other sea-urchin (Lepidesthes colletti and extremis), so that in the number of columns at 

 the ambitus this species surpasses all known Echini. Dorsally, next to the oculars there are 



