SYSTEMATIC ( I.ASSII'K'ATION OF K MINI. 



composed of many rather thick plates close to the character of tin- peripnx-t in the < 'idan.ida. 

 The lantern is known well for the Palaeozoic only in (\n> order, and i.- -trikinnly uniform in 

 character. Mr. Agassiz (1881, p. 80) suggested and Duncan (1889a, p. 1 1 tated that there 

 are passages for peristomal gills in Archaeocidaris, but such have not been (inured. A- th.-n- 

 was no indication of such slits in the best specimens which I studied i Plate '., fin. (i and Plato 

 11, fig. 1) and as such structures are otherwise known only in the ( Vntrerhinoida and Holee- 

 typina, I think this is a mistake, and peristomal gills may be considered a- \\ anting in 

 Archaeocidaris and other Palaeozoic genera as well (p. 253). 



The Archaeocidaridae is a family with only three genera, Eocidaris, Archaeocidark and 

 Lepidocidaris. Eliminating Eocidaris, which is most imperfectly known, there are two column* 

 of ambulacral plates and four, or six to eight of interambulacral plates in each area resort ively. 

 The plates are rather strongly imbricate, and each interambulacral plate bears a central pri- 

 mary perforate tubercle and large spine, also secondary spines and tubercle-. The base of tin- 

 corona is extensively resorbed, there being four plates in the basicomnal row in each interambu- 

 lacral area. The peristome has many rows of ambulacral plates with iion-ainbularral plate- 

 in Archaeocidaris (Plate 9, figs. 6, 7) and probably was similar though unknown in Ix-pido- 

 cidaris. The apical system is doubtfully known, which is rather remarkable with so many 

 species. The lantern is well known in Archaeocidaris (Plate 12) and con-i-ts of forty | 

 as in modern regular Echini (p. 254). 



The genus Eocidaris has large interambulacral plates which bear a central perforate 

 tubercle, as in Archaeocidaris; there is a scrobicular area but no basal terrace. Thi> genus i- 

 most imperfectly known, but Bather (1909), who has studied the question and material crit ically . 

 feels that it should be retained. Only one species is recognized, the Devonian K. Inerifirinn 

 (Sandberger), Plate 15, figs. 11, 12. The absence of a basal terrace, which is the essential 

 difference from Archaeocidaris, could easily be accounted for by wear as it is not always ob- 

 servable in true Archaeocidaris. The young dorsal plates of Archaeocidaris have no basal 

 terrace (Plate 11, fig. 2), so that a genus founded on this character should be considered the 

 more primitive of the two (p. 254). 



In Archaeocidaris the ambulacral plates are narrow and low, with pore-pairs uniserial 

 (Plate 12, fig. 9). In the few species where the corona is fairly known, there are four columns 

 of large plates in each interambulacral area (Plate 10, fig. 10). Each plate bears a large mitral 

 perforate tubercle with a basal terrace and scrobicular ring (Plate 11, fig. 4). The basal terrace 

 is so slight an eminence that it is often worn off, and this feature can only \> ascertained in 

 fairly well preserved specimens. From the center rises a primary spine of ronsiderabl. 

 and various ornamentation; in addition, secondary and miliary spines and tubercle- occur 

 on the periphery of the plates. The young plates dorsally i Plate 1 1 . fig. 2) are at first smooth, 

 then an imperforate tubercle arises (as in developing plates of cidarids, Plate 3, figs. 1, 



