SHALLOW-WATER STARFISHES 331 



Ctenodiscus corniculatus Perrier, Stell. du Mus., p. 380, 1875 (after Linck). 



Duncan and Sladen, Echinod. Arctic Sea, p. 49, pi. in, figs. 17-20, 1881. 



Sladen, Voy. Chall., p. 171, 1889. Doderlein, op. cit., p. 221, pi. ix. figs. 



2, 3, 1900. 

 Ctenodiscus krausei Ludwig, Zool. Jahrb., Syst., i, p. 290, pi. vi, figs. 13-16, 



1886. 

 Ctenodiscus crispatus Fisher, op. cit., 19116, p. 31, pi. in, figs. 1-4; pi. iv, figs. 



1-6. 



The following description is from Alaskan specimens. Disk 

 broad, thin, with regularly curved interradial margins, which are 

 bordered by the summits of the thin upper ends of the upright 

 superomarginal plates, each of which usually bears a small conical 

 spine. 



Rays five (rarely four), broad at base, rapidly tapered, subacute, 

 varying considerably in length, relative to disk. Radii of a specimen 

 from off Chilikoff, Alaska, are 14 mm. and 24 mm. ; ratio, i : 1.7. 



Another, from the same place, has the radii 12 mm. and 23 mm. ; 

 ratio, i: 1.9. These are of mediimi proportions; the ratios of the 

 radii are often i : 2, and up to i : 2.25. 



The dorsal paxillse are minute and pretty uniformly crowded over 

 the whole surface. Madreporite rather large and conspicuous. 

 Ocular plate rather large, shield-shaped, longer than broad, distal 

 end notched. 



The upper marginal plates are closely united to the lower ones, 

 end to end, so that the fascicles between them coincide ; those in the 

 interradial areas extend but slightly on the disk, but the small distal 

 ones encroach considerably on the upper side of the rays. The mar- 

 ginal spine is short, subacute, articulated on a central mammilliforni 

 tubercle, which shows a central pit when the spine is removed. The 

 tubercle is wider than the median naked keel of the plate, except 

 distally on the rays, where the keel becomes wider. The fasciolated 

 spinules are longer than the width of the keel, except distally on the 

 rays; they are flat, and project at nearly right angles to the edges of 

 the keel and parallel to the surface of the plate ; they form a single 

 regular close row, with a small, well defined channel under them. 

 This channel extends down between the inferomarginal plates, with 

 the same sort of fasciolated spinules ; but the latter gradually become 

 shorter downward, and point obliquely upward. 



The inferomarginal plates of the interradial arcs are considerably 

 shorter, vertically, than the upper ones, and have the naked median 

 keel more than twice as wide, while toward the ends of the rays it 

 becomes much wider, covering most of the squarish plates, the 



