210 THE VOYAGE OF H.M.S. CHALLENGER. 



do not possess the characters diagnosed by Dr Norman in the description of his Astro- 

 pecten acicularis. 1 I have therefore referred them to the older type. 



Sir Wyville Thomson 2 expresses very definitely his belief that Astropecten acicularis 

 is merely a deep-water variety of Astropecten irregularis ; and states that a magnificent 

 series was procured by Mr Waller in 1869 during a dredging cruise off the south coast of 

 Ireland, showing a gradual transition through all intermediate stages between the large 

 and the small varieties. 



10. Astropecten pontoporseus, Sladen (PI. XXXV. figs. 1 and 2 ; PI. XXXVIII. figs. 

 10-12). 

 Astropecten jjontoporseus, Sladen, 1883, Journ. Linn. Soc. Lond. (Zool.), vol. xvii. p. 259. 



Rays five. E = 53 mm ; r= 15 mm. R = 3'5 r. Breadth of a ray at the base, 16'5 

 mm. 



Rays rather broad throughout, and only slightly tapering until near the extremity, 

 which, although pointed, is rather obtuse. Interbrachial arcs subacute, or with a faint 

 tendency to rounding. 



The paxillar area is wide and extensive, with numerous, rather small, compact paxillaB. 

 The spinelets of which these are composed are short and uniform. The larger paxillse have 

 a circlet of twelve to fourteen spinelets surrounding seven or eight on the centre of the 

 tabulum ; and the smaller paxillse present about half these numbers. Along the sides of 

 the rays the paxillse are arranged in regular transverse lines, about five or six in each. 

 The paxillse diminish greatly in size in the neighbourhood of the centre of the disk and 

 towards the ends of the rays. 



The supero-marginal plates, which are twenty-seven or twenty-eight in number from 

 the median interradial line to the extremity, are broader than long ; and their height is 

 about equal to the breadth at mid-arm, but greater on the inner portion of the ray. The 

 plates are well-rounded and tumid, which gives them a crested or subtubercular appear- 

 ance, and clearly defines the separate plates. The plates are covered with small papilliform 

 granules, which decrease in size towards the margins ; and each plate normally bears an 

 elongate granule or aborted spinelet, situated rather low down on the curve which unites 

 the abactinal and lateral surfaces of the plate ; but not unfrequently two or three may be 

 present, and these stand in transverse line along the median line of breadth. 



The infero-marginal plates are broad, rather sharply rounded towards the actinal sur- 

 face, and do not protrude beyond the level of the superior series. Each bears four or five 

 lateral spines standing in an oblique line, only slightly inclined to the axis of the ray, 

 passing from the adoral to the aboral side of the plate. The spines are short, cylindrical, 

 tapering, and pointed ; the third or fourth from the adoral end of the line is the longest, 



1 Ann. and Mag. Nat. Hist. 1865, ser. 3, vol. xv. p. 116. 



2 The Depths of the Sea, 1873, p. 121. 



