MACCOYA. 313 



Palaeechinus burlingtonensw Loven, 1874, p. 41; Duncan, 1889, p. 205. 



Maccoya burlingtoncnsis Pomel, 1883, p. 115; Lambert and Thicry, 1910, p. 119. 



Rhoechinus burlingtoncnsis Jackson, 1896, p. 203, Plate 7, fig. 37; Tornquist, 1897, p. 7(12; Klnii, 1904, p. 27. 



The test is spheroidal. In Mr. Kirk's specimen (Plate 32, fig. 2) the ambulacrum is 5 mm. 

 wide, interambulacrum 18 mm. wide at the mid-zone. From these measurements the circum- 

 ference would be about 115 mm., the diameter about 37 mm., and the height as estimated is 

 very nearly the same. A specimen in the Museum of Comparative Zoology, no. 3,011, is com- 

 plete in form and very nearly spherical. It is about 36 mm. in diameter at the mid-zone and 

 a trifle more than that when measured through the poles. The ambulacrum is 5.5 mm. wide 

 and the interambulacrum about 17 mm. wide at the mid-zone. 



The ambulacra are narrow, with two columns of low plates in each area. All ambulacra! 

 plates meet the middle of the area, but at the mid-zone, on the exterior, alternate plates are 

 primaries, reaching and enlarged at their contact with the interambulacrum; or plates are oc- 

 cluded, being narrowed and cut off from interambulacral contact. The pore-pairs at the mid- 

 zone are biserial (Plate 33, fig. 2). While this is the character of the exterior, on the interior a dif- 

 ferent and more primitive condition exists, for here all plates cross the half-area without marginal 

 modification, and pore-pairs are uniserial, as seen in external and internal views of the very 

 same plates (Plate 33, figs. 4, 5). On the exterior, the plates ventrally, built in the youth of 

 the individual, and also dorsally the young plates, as a localized stage, are all simple primarir-, 

 completely crossing the half-area and with pore-pairs uniserial (Plate 33, figs. 1, 2). This 

 simplicity of plates built in youth, of young plates dorsally, and of plates at the mid-zone .-ecu 

 from within, is directly comparable to the simplicity of all plates in the more primitive grim.- 

 Palaeechinus (p. 60). Ambulacral plates bevel over the adambulacrals on the marginal suture. 



There are four columns of plates in each interambulacral area at the mid-zone, as shown 

 in twelve specimens. Ventrally, as seen clearly in one of Mr. Springer's fine series of specimens 

 (Plate 32, fig. 1 ; Plate 33, fig. 1), there are two plates in the basicoronal row, three in the second, 

 and four in the third row, above which no more columns are added. The same structure is 

 shown ventrally in a large specimen in the Museum of Comparative Zoology (3, 194), only in this 

 individual the initial pentagon of column 4 is on the left of the center in the third row instead 

 of on the right of the center. It is interesting to see that in this species with only four columns 

 of interambulacral plates, as also in Palaeechinus quadriserialis (Plate 30, fig. 3), that the fourth 

 column originates in the third row from the peristome as it does throughout the family with 

 very rare exceptions. In burlingtonensis the adradial plates are pentagonal, all others hexag- 

 onal, excepting ventrally where new columns are coming in. Ambulacral and interambula- 

 cral plates alike bear numerous small secondary tubercles, shown beautifully in Mr. Kirk's 

 choice specimen (Plate 32, fig. 2). Meek and Worthen figure a spine enlarged showing that 

 it is swollen at the base, slender, tapering, and, judging from the figure, about 4 mm. in length, 



