328 ROBERT TRACY JACKSON ON ECHINI. 



they are at all different from the small secondary or, possibly better, miliary tubercles in other 

 species of this family. The dorsal portion is not figured or described by Julien. 



Tornquist next took up this species and published a detailed description of his specimens, 

 with excellent figures, including a good restoration of the whole test. He shows (my Plate 38, 

 figs. 1-3) that there are four columns of ambulacral plates as the species character, wide occluded 

 and narrower demi-plates, with pore-pairs in peripodia, biserial, situated near the interambula- 

 crum on the exterior, but near the middle of the half-area on the interior of the test. He shows 

 that ventrally ambulacral plates are primaries, of equal width, with pore-pairs uniserial. There 

 are four columns of interambulacral plates in an area, and both these and the ambulacrals 

 bear small secondary tubercles. 



In the British Museum there are two specimens clearly referable to this species, from 

 Armagh, Ireland, numbers E 10,052 and E 10,053. In the larger of these (Plate 35, fig. 5; 

 Plate 36, figs. 4, 5) the ambulacrum at the mid-zone measures 7 mm. in width, the interam- 

 bulacrum 16.5 mm. From these measurements the circumference would be about 117.5 mm. 

 and the diameter about 37 mm. The height is about equal to the diameter. The ambulacra 

 are narrow and at the mid-zone have four columns of narrow demi- and wide occluded plates, 

 the pore-pairs are biserial, lying near the next adjacent interambulacrum. Interambulacra are 

 wide, with four columns of plates in two areas, seen dorsally only in area A. The plates are 

 pentagonal adradials and hexagonal in the median columns. A hexagon at the mid-zone 

 measures 5 mm. in width by 4.2 mm. in height. Dorsally, in area A, a genital plate in place is 

 high, wide, with three genital pores. The second specimen from Armagh (Plate 35, fig. 4; 

 Plate 36, fig. 6) presents the dorsal portion only. The ambulacrum is similar to the last, and 

 there are four columns of plates in three interambulacral areas. The most important feature 

 is the apical disc, unknown in the type specimen. There are three oculars in place which are 

 small and triangular in form, and all are fully exsert. Oculars D and F are as fully excluded as 

 is ocular B (the drawing being not quite correct in this point, as I have recently ascertained by 

 examining the specimen). The oculars cover the ambulacra and in area E the interambulacra 

 in part on either side as usual. They do not impinge on the interambulacra in areas A, G, 

 and in the left side of C, but this lack is ascribed to local disturbance in fossilization, as I 

 have found so universally that oculars do reach the interambulacra in Echini (p. 86). The 

 genitals are high and wide, and three have three pores each, but one has only two pores. This 

 specimen was labeled " Palaechinus sphaericus " and it is probably the one referred to by 

 Duncan (1889, p. 196) as Palaeechinus sphaericus of which he says that the oculars are all 

 excluded from the periproct (p. 320). 



A specimen from Helsington Barrows, in the Museum of Practical Geology Collection 16,301, 

 is ascribed to this species (Plate 36, figs. 1-3). The ambulacra are narrow, with four columns 

 of demi- and occluded plates at the mid-zone, and pore-pairs are biserial. Ventrally, near the 



