278 ROBERT TRACY JACKSON ON ECHINI. 



The imbrication of plates in this species was described by Professor Young, who, I believe 

 was the first to show that this character occurred in Archaeocidaris. 



A specimen from Fermanagh, North Ireland, in the Jermyn St. Museum, no. 7,659 (Plate 14, 

 figs. 20a-c), shows interambulacral plates with prominent tubercle, basal terrace, secondary 

 tubercles, and strong radial plications which extend inward from the margins of the plate ; also 

 a characteristic primary spine with its strong spinules extending distally from elevated ridges. 

 The longest spine measures 64 mm. in length, is longitudinally finely striate and thickly set 

 with spinules. This specimen is of importance as it is the original holotype of Portlock's Cidaris 

 benburbensif from whose figures mine are taken. Portlock (1843, p. 353) gives the locality as 

 Benburb, boundary of Armagh and Tyrone. This may be the correct locality of this type ; 

 but Fermanagh is the locality given on the old original label in the Jermyn St. Museum. Dr. 

 Kitchin tells me that the matter of the locality for this specimen is open to question. Port- 

 lock may have been mistaken, or some error may have crept into the label before the 

 day of catalogues. 



A fine specimen from Millstone Neuk, Dunbar, Scotland, in the Jermyn St. Museum, 

 is of interest from the very perfect condition of preservation of the spines. The longest of 

 these, which is not quite complete distally, measures 61 mm. in length. The spinules are 

 beautifully preserved, measure about 1.5 mm. in length, and are set at an angle of about 45 

 from the axis of the shaft, pointing distally. 



A specimen from Corwen, Wales, in the Sedgwick Museum, Cambridge, England, shows 

 the surface characters of interambulacral plates very clearly, as figured by Keeping, from whom 

 my figures (Plate 14, figs. 19 a-c) are taken. Of these plates, several show the basal terrace 

 and radial plications extending inward from the margins. A peculiar elongate plate occurs 

 in this specimen (Plate 14, fig. 19c), the nature of which is doubtful. As it has a perforation 

 near one end, it is possibly a genital plate, but genitals are so far not definitely known in the 

 genus (pp. 265, 266, 414). 



The species Cidaris vetusta Phillips, as suggested by M'Coy (1844), may be reasonably 

 referred to urii as a synonym. Phillips described the spines as rudely muricate, and Portlock 

 described them as having four or more rows of strong prickles. A specimen from the Portlock 

 Collection, from Fermanagh, Ireland, in the Jermyn St. Museum, no. 16,321, bears the old 

 manuscript label Cidaris vetusta. It is doubtless the specimen referred to by Portlock (1843, 

 p. 353) from this locality, but is not the original of his Plate 16, fig. 11. The spines and plates 

 of this specimen are not distinguishable from urii, though in the plates the radial plications are 

 only faintly preserved. Another specimen from the Portlock Collection, from Clogher, County 

 Tyrone, Ireland, in the Jermyn St. Museum, no. 7,768, consists of two interambulacral plates 

 on a slab with other fossils. This specimen is probably the one referred to by Portlock (1843, 

 p. 353) from this locality, and one of the plates corresponds so closely with that figured by 



