PALAEECHINUS. 309 



spheroidal, in the type somewhat crushed, but it measures about 55 mm. in width, the ambula- 

 crum at the mid-zone is 5 mm. in width, the interambulacrum 24 mm. in width. 



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

 all primaries, meeting the interambulacra and the middle of the ambulacra throughout the 

 areas; pore-pairs uniserial. Five or six ambulacral plates equal the height of an adambul- 

 acral. There are five columns of interambulacral plates at the mid-zone in each area in all 

 specimens seen. The ventral portion of the test unknown, but it is doubtless similar to that 

 of Palaeechinus quadriserialis, Plate 30, fig. 3. Ambulacral and interambulacral plates with 

 numerous secondary tubercles which bear small spines, swollen at the base, tapering to the tip, 

 all of similar size and measuring about 1.1 mm. in length. Oculars are insert, imperforate 

 (not with two pores as described by Baily) ; genitals are wide, high, with three or more genital 

 pores each. The periproct in the type is remarkably well preserved, with many small angular 

 plates like those of modern cidarids. The apical disc and periproct figured by Baily (1865b, 

 Plate 4, fig. B) were freely and in some respects incorrectly restored (p. 363). 



Lower Carboniferous, Hook Head, County Wexford, Ireland; slab with two specimens 

 including the holotype in the Griffith Collection, Science and Arts Museum, Dublin; a cast 

 of this specimen is in the Museum of Comparative Zoology Collection 3,116; same locality, 

 Museum of Practical Geology, London, 6,580; Putig, Germany (Tornquist); Marbre Noir de 

 Dinant, Belgium (Fraipont). 



The most nearly complete specimen known is M'Coy's type, which is one of two specimens 

 of this species on a slab in the Dublin Museum. I had the pleasure of studying it there and 

 in addition, Dr. Scharff had the great kindness to bring it with him to America in order to give 

 me further opportunity for inspection. Besides the two specimens of Palaeechinus ekgans, 

 this choice slab bears a specimen of Perischodomus biserialis (Plate 29, fig. 5). Baily (1865b, 

 p. 63) in his observations says that there are three specimens of Palaeechinus ekgans, but this 

 is a mistake, the specimens being as stated. One of the specimens of P. elegans is better than 

 the other, and is the basis of M'Coy's and Baily's observations. Ambulacra D and J extend 

 directly to the oculars, and F is preserved in part. The ambulacra bevel over the adambul- 

 acrals laterally (Plate 31, fig. 3). Interambulacrum E is the most nearly complete and shows 

 five columns of plates, but dorsally, column 5 (Plate 31, fig. 4) drops out before reaching the 

 apical disc. The surface of the plates is in part worn, but I have shown the small secondary 

 tubercles in the parts where such occur. Interambulacra E and I (Plate 31, fig. 4) evidently 

 have each five columns of plates, although one of the adradial columns is partially wanting 

 in each of these areas. Dorsally four oculars are in place, but ocular F is imperfect and not 

 shaded in the figure. The oculars are all insert, covering the ambulacra and laterally in part 

 the interambulacra on either side. The oculars are imperforate, and Baily's (1865b, Plate 4, 

 fig. B) figure showing two pores in each plate was a mistake. I cannot see how it occurred. 



