EUGASTEH. 209 



nating row of stout ambulacral plates (probably thirty in number) excavated on 

 their outer margins by large round pores, which are bounded outside by elongate, 

 curving or bent, adambulacral plates. Surface of plates minutely granulated. 

 Oral plates large, wedge-shaped, paired into close connection at their apices. 



Size. An arm measures 28 mm., so that the expanded animal must have 

 measured about 50 mm. 



Localities. In the Museum of Practical Geology are three specimens from 

 Croyde, and one (cast and reverse) from North Devon; in Mr. Hamling's Col- 

 lection one (cast and reverse) from Top Orchard Quarry ; and in the Porter 

 Collection an indistinct specimen from Fremington. 



Remarks. While these specimens have much resemblance to those last 

 described, several dissimilarities are to be noted in them. Thus the disc (usually 

 very indistinctly seen) appears much larger and covered by much smaller plates, 

 the rosette seems larger, the arms stouter and more quickly tapering, and the 

 ambulacral plates much broader. In some of the specimens the adambulacral 

 plates appear to have been pushed out of place. At the same time it does not 

 seem certain, in the defective state of our specimens, how much real value these 

 dissimilarities have, whether they are partly caused by their imperfection, or are 

 indicative of a specific difference. It has seemed advisable, therefore, to keep 

 them separate for the present, as an unnamed variety of the former species. 



2. Genus EUGASTER, Hall. 

 1. EUGASTER ? PERARMATUS, Whidborne, sp. Plate XXVII, figs. 4 6 a. 



1896. PBOTASTEE PEBAEMATUS, Whidborne. Proc. G-eol. Assoc., vol. xiv, p. 377. 



Description. Animal large. Upper surface of the plates of the disc and arms 

 minutely granulated. Arms very stout, rather rapidly tapering, covered on the 

 upper surface by a median row of broad, convex, subhexagonal plates (which 

 seem slightly to imbricate inwardly) alternating on each side with a row of still 

 wider subpentagonal plates, which in their turn are followed by a row of smaller 

 plates on the perpendicular sides, bearing at their lower extremities long lateral 

 spines at the rate of two or three to each plate. Spines thorn-like and probably 

 about the width of the arms in length. Under side with a double row of level 

 ambulacral plates, succeeded on each side by a row of narrow adambulacral 

 plates, which are separated from the former by very large transverse hexagonal 

 excavations, of which probably only the outer portions are occupied by the pores 

 themselves. 



