50 ON THE ECHINODERMATA OF THE 



1875. Ctenodisciis corniculatus, Perrier, Stellerides du Museum, p. 380; Arch, de Zool. oxp. et gen. 



p. 300. 

 1879. Ctenodiscus corniculatus, Viguier, Squelette des Stell., Arch, de Zool. exp. et gen. t. vii. p. 226. 



Body depressed and goniodiscoid in outline ; radii five in number, with the arm- 

 angles well rounded ; proportion of greater to lesser diameter 2 : 1. The calcareous 

 elements of the abactinal surface form a compact network, similar to Astropecten, in 

 which the interspaces are but very small. A great number of small closely-placed 

 paxillas are borne upon this framework, each carrying 5-10 round, blunt spinelets, the 

 whole so densely crowded together that the spinelets are normally directed upward 

 from the pedicle. The abactinal surface is frequently puffed up and more or less 

 convex in profile (owing probably to the quantity of sand or clay with which this Star- 

 fish fills its stomach) ; whilst a small peak-like protuberance rises from the centre, 

 around which the paxilla? rapidly diminish in size. The sides of the disk are perpen- 

 dicular, and formed of two series of marginal plates one ventral, the other dorsal. Each 

 dorsal plate is ankylosed to a corresponding ventral plate the pair thus formed being 

 separated from the neighbouring pair on either hand by a deep furrow, which follows the 

 lateral suture of the plates, the margins being fringed with a series of fine, compressed, 

 cilia-like spinelets, which arch over the furrow. Each of the dorso-lateral plates bears 

 a small compressed, but pointed, spinelet, which stands erect on its upper margin ; and 

 the lower or ventro-lateral series likewise carry a similar spinelet, which is placed near 

 the junction of the ventral and dorsal plates, and projects at right angles to the side 

 walls of the test. The last or terminal dorso-lateral plates of each side of a ray are 

 ankylosed together, and form a large arched or tubercular plate, indented on its outer 

 margin, and bearing three more or less prominent tubercles the rudiments of dorso- 

 marginal spines. The furrows between the marginal plates are continued onto the 

 actinal surface of the animal and extend to the ambulacral furrow, cutting up the 

 ventral interradial areas into band-like spaces, each of which is tessellated with irregular, 

 subquadrate, scale-like plates that imbricate upon one another, and form normally, in 

 large adult examples, a double alternating series behind each adambulacral plate. The 

 innermost band, however, of each area comprises two adambulacral plates ; and the 

 trapezoid tessellating scales, which here always form a regular double alternating series, 

 are, in consequence, twice as large in the neighbourhood of the furrow as the scales in 

 the other bands. All these plates bear on the margin that opens on the sutural furrow 

 a series of papilla? that form a continuation with the papillae above-noted on the sides 

 of the lateral plates, from which they differ only in being not flattened, nor are they at 

 the same time so regular and closely placed. The adambulacral plate presents a wedge- 

 shaped projection into the furrow, and carries five or six papillae, three only of which 

 usually stand on the margin of the ambulacral furrow, the remaining two or three 

 (which are generally much smaller) being situated on the aboral margin opening on the 

 sutural furrow of the interbrachial area ; not unfrequently, however, one of them is as 

 large as the ambulacral spinelets, and is placed somewhat inward upon the plate, away 

 from the sutural fringe and behind the ambulacral series. Towards the extremity of 



