MACCOYA 311 



In the Museum of Comparative Zoology's specimen (Plate 29, fig. 8) there are six columns 

 of plates in four interambulacral areas, but only five columns in one area. Oculars are all 

 insert. The apical disc measures 8 mm. in diameter equaling about 21% of the diameter 

 of the test. This is relatively larger than in adults of most species of the family, but is the 

 same proportion as in the young of Lovenechinus missouriensis (p. 342). In Mr. Kirk's speci- 

 men (Plate 32, fig. 7) there are six columns of plates in all five interambulacral areas. This 

 species is the only one in America at present referable to Palaeechinus proper. 



Base of the Burlington Limestone, Lower Carboniferous, Burlington, Iowa, holotype. 

 University of Chicago Collection 9,054; paratypes, Museum of Comparative Zoology Collec- 

 tion 3,051; E. Kirk Collection, one specimen; F. Springer Collection, two specimens. 



Maccoya Pomel. 



MacCoya Pomel, 1S(J9, p. xlvi. 



Wrightia Pomel, 1S79, p. xlvi (printed by error Wrigthia); Pomel, 1883, p. 115; non Agassiz, 1S62, Acalephs, 



Diseophora, p. .354. 

 Macroija Pomel, 1883, p. 115; (pars) Lambert and Tliiery, 1910, p. 119. 

 Wrifjhtclla Pomel, 1883, p. 115; Lambert and Thiery, 1910, p. 120. 

 Non Erirchinus Pomel, 1883, p. 114 (see footnotes, pp. 303, 312, 32G). 



Non Tijphlechimis Neumayr, 1889, p. 3(52, text-fig. 82e; 1890, p. 85 (see footnotes, pp. 312, 32(3). 

 Palarrchinus (pars) Duncan, 1889, p. 205; 1889a, p. 13; (pars) Jackson, 1896, pp. 200, 239 (see this 

 memoir, p. 303). 



Palacchinm (pars) Kiem, 1904, p. 31; (pars) Lambert and Thiery, 1910, p. 119. 

 Palrchiini.i (pars) Tornquist, 1897, p. 735. 



The test is spheroidal, ambulacra are narrow, composed of two columns of plates in each 

 area, all plates meet the middle of the area, but at the mid-zone alternate plates are primaries, 

 meeting the interambulacral areas and enlarged marginally, while the plates between are nar- 

 rowed laterally and are nearly or quite cut off from contact with the interambulacra by the 

 marginal enlargement of their fellows (Plate 34, fig. 2). There are two pores to each plate ' 

 and the pore-pairs are biserial. All this is as seen on the exterior; on the interior at the mid- 

 zone and throughout the area all plates cross the half-areas and pore-pairs are uniserial (Plate 

 33, figs. 4, 5, 7, 8). As seen from the exterior, ventrally the ambulacral plates built in youth 

 as a stage in development, and also young plates dorsally near the apical di.sc, as a localized 

 stage, are all typical primaries crossing the half-areas and with pore-pairs uniserial. This 

 is like the condition characteristic of the mid-zone in the lower genus Palaeechinus. 



The interambulacra in the known species have in each area from four to eight, or excep- 

 tionally nine columns of plates at or above the mid-zone. The peristome and lanterns are 



'Miss Klem (1904, p. 31) .says of Palaccliinu.s [Maecoya], four pores in each ambulacral plate. This is a character 

 not known in the genus nor in any Palaeozoic echinoid. 



