306 ROBERT TRACY JACKSON ON ECHINI. 



The test is high .elliptical; according to Wright, the type measures 51 mm. in height and 

 38 mm. in diameter. The British Museum specimen measures about 42 mm. in height and 

 about 34 mm. in diameter through the mid-zone. The ambulacra measure 4.5 mm. in width 

 near the mid-zone, and the interambulacra 17 mm. in width. 



The ambulacra are narrow with two columns of low plates in each area, all of which meet 

 the middle of the area and the interambulacrum ; about five ambulacral plates equal the height 

 of an adambulacral; pore-pairs are uniserial. Ambulacral plates bevel over the adradials on 

 the marginal sutures. The interambulacra are wide with four columns of plates at the mid- 

 zone in each area. There are two plates in the basicoronal row, above which the added columns 

 come in early, and there is no loss of parts by senescent growth dorsally. Plates of the test 

 are moderately thick, bearing numerous secondary tubercles only; spines are not known. 

 Oculars are all insert, imperforate, and cover the ambulacra and laterally in part the inter- 

 ambulacra on either side. Genitals are high and wide, each known having three genital pores. 

 This species is similar to ellipticus in form, but differs in having four instead of five columns of 

 interambulacral plates. It is also a much smaller species. Baily (1865a, 1865c) described a 

 specimen of this species as P. ellipticus, as he felt that the difference in the number of inter- 

 ambulacral columns did not entitle it to specific distinction. A difference in the number of 

 interambulacral columns is a valid differential character, and I think these two species should be 

 maintained. Baily's use of ellipticus for quadriserialis was quoted by Loven, and his figure 

 was copied by Quenstedt as given in the synonymy. 



Lower Carboniferous Limestone, Middleton, County Cork, Ireland. This is the locality 

 of the type, but I do not know where the specimen is; the specimen figured by Baily is from 

 Betty ville, near Crome, County Limerick, Ireland; the specimen in the British Museum Col- 

 lection E 193 is from Rathkeale, County Limerick, Ireland; Hook Head, Ireland, Museum 

 fur Naturkunde, Berlin, a cast of this specimen is in the Museum of Comparative Zoology 

 Collection 3,117. 



The British Museum specimen of this species is well preserved, so that it is represented 

 spread out by the Lov6n method in Plate 30, fig. 3. It agrees entirely with Wright's descrip- 

 tion and excellent figures of the species. It is preserved without distortion and free from all 

 matrix. In parts the plates are in place, as shown in Plate 30, figs. 1, 3, 4, and at these parts 

 the tubercles are shown. Much of the rest is preserved as an internal mold of the plates by 

 the filling matrix, and in the figures is represented in simple outline; again, part is restored as 

 indicated by dotted lines. There are two plates in the basicoronal row in each interambula- 

 crum and three plates in the second row. In all areas excepting C the initial plate of column 3 

 is hexagonal as usual, as it is in contact with the initial plate of column 4. But in area C the 

 initial plate of column 3 is pentagonal, as the initial plate of column 4 is in the second row above, 

 instead of the next row. Column 4 originates in the third row in four areas with a pentagonal 



