PROTOCIDAKIS. 203 



our species may be compared. In Hall's definition of the genus and of the type 

 species (L. imbricatus) no tubercles are mentioned. In his second species, L. rari- 

 spinus, 1 a few of the interambulacral plates bear very much, elevated tubercles. 

 The characters of these tubercles are not very evident from the description of the 

 species, but judging from the figure it seems extremely unlikely that they tally 

 with ours. 



It therefore is most probable that its genus is distinct, although at preseut this 

 can be only very imperfectly defined. 



1. Protocidaris acuaria, Whidborne, sp. Plate XXV, figs. 1 — 2 a. 



189(3. Eocidaris ? actjaria, Whidborne. Proc. Geol. Assoc, vol. xiv, p. 376. 



Description. — Interambulacral plates large, 4 or 5 mm. in diameter (probably 

 sometimes hexagonal in shape), bearing a small central perforated tubercle 

 consisting of a mamelon surmounting a boss, but without any distinct areola, and 

 surrounded by an irregular circle of five or six minute granules or warts. Spines 

 cylindrical, of various sizes, sometimes being more than 11 mm. long, finely 

 striated longitudinally, but without lateral spicules, and slightly constricted above 

 the base, which is expanded in the shape of an inverted truncated cone. Dental 

 apparatus large, apparently more than 30 mm. in size, some of its ossicles being 

 covered on one side with transverse, and on another with obliquely rugose, 

 markings. 



Size. — The test was probably very large, a fragmentary specimen, which shows 

 comparatively few plates, being about 65 mm. in length. 



Locality. — In the Museum of Practical Geology are three fragmentary 

 specimens, all probably portions of a single animal, from " East of Barnstaple." 



Remarks. — The only specimens of this species with which I am acquainted 

 yield but very imperfect information about its characters. They consist of the 

 casts of confused groups of plates and spines, the latter having helped to obscure 

 the shape of the former. I have not recognised any ambulacral plates among 

 them, and it is therefore probable that the ambulacral areas occupied a compara- 

 tively small portion of the test. Though the margins of the plates are for the 

 most part obliterated, their general size and character are clear, and, with the 

 following exception, I have not been able to recognise anything very similar to 

 them in the descriptions of recorded species. 



Cidaris Isevispina, Sandberger, 2 which Desor 3 refers to Eocidaris, though 



1 1867, Hall, ' Twentieth Report Kegents Univ. N. Y.,' p. 295, pi. ix, fig. 10. 



2 1856, Sandberger, ' Verst. Ehein. Nassau,' p. 382, pi. xxxv, figs. 2 — 2b. 



3 1858, Desor, ' Synopsis Echinides IWiles,' p. 156, pi. xxi, figs. 18—22. 



DD 



