TH. MORTENSEN, ECHINOIDEA 



1. Phyllacanthus longispinus n. sp. 



I'l. I— II; Pl. III, Fig. 2; Pl. V, Fig. 15. 



There are only two dried specimens of this species, both in rather poor con- 

 dition. One of them (specimen a) is broken in two pieces, but fortunately in such 

 a way that it could be bound together to be photographed (Pl. I). The figures of 

 this and the other specimen (b) (Pl. II) conve}' a good idea of what a magnificent 

 species this is. 



I. Arabulaora Ambulacra Longpst 



Horiz. Diam. Height. Apioal Area Peristome Width No. of plates Width No. of plates Radioles 



Specimen a. 85 min 52 mm 30 mm ? 45 mm — 7 7 mm 21 — 22 105 — 7 mm 



» b. 78 » 50 » 28 » :55 mm 44 » 6—7 8 » 21—22 103 » 



The specimen a is only labelled N.W. Australia, specimen b Cape Jaubert. 

 That both are littoral, is probable, but there is no information about them. It 

 would be interesting to knovv whether this species, vvith its immense radioles, is 

 able to conceal itself under rocks and in crevices in the same way as Ph. parvispinus, 

 which is found in such places, often in places so narrow, that one cannot help 

 wondering how it could get there with its big, clumsy spines. 



The very long primary radioles are fairly slender, very nearly cylindrical, only 

 slightly attenuated tovvards the point, which is fluted as usually in Phyllacanthus. 

 They are finely striated-tuberculated, the tubercles being distinctly serially arranged. 

 The adoral radioles are somewhat clubshaped (Pl. II). The ambulacral marginal 

 spines are thin and cylindrical with merely an indication of a flattening at the tip. 

 differing considerably from the distinctly widened and flattened marginal ambulacral 

 spines of the other species of this genus. The small spinelets covering the apical 

 area and the median space of the ambulacra and interambulacra are quite short, 

 thick, as is usual in this genus. 



The median ambulacral area is occupied by four rovvs of small spines (tubercles) 

 in specimen b; in specimen a there are only quite exceptionally more than two rows 

 of small spines in the median area, which thus looks less crowded than in the other 

 specimen. The median interambulacral area is fairly broad. 



Apical area. The ocular plates are all widely separated from the anal area. 

 The genital pore is on the top of a very conspicuous conical elevation (Pl. III, Fig. 

 2); the spines on it are quite small, as are those on the middle of the genital plate. 

 The elevation is thus not produced by larger spines surrounding the genital ope- 

 ning, as is the case in Phyllacanthus magnijicus H. L. Clark. In the other species 

 of the genus there is no such elevation. It is somewhat more conspicuous in speci- 

 men b than in specimen a, but it is quite distinct also in the latter specimen. 



