336 THE VOYAGE OF II. M.S. CHALLENGES. 



of a pedicle with a slightly expanded base and a rounded clavate extremity, on which the 

 spinelets that form the crown are articulated. The expansion of the base of the paxillae 

 is very slight, subcircular, or irregular in outline, and usually exhibiting two or three 

 faint prolongations. The bases of the paxillse are closely placed, and occasionally a trace 

 of overlapping may be found here and there. This structure is identical with that met 

 with in the Astropectinklrc, and has hitherto been looked upon as specially characteristic 

 of that group. 



The adambulacral plates, their armature, and the mouth-plates have strictly the 

 characters of the Pentagonasteridse. The marginal plates are likewise suggestive of 

 the same group, and, notwithstanding their inequality and insignificant development, 

 approach the habit of such forms as Gnathaster paxillosus, Gray, sp., from which also 

 the general outline of the body of Mimaster tizardi is not far removed. 



The actinal intermediate plates recall in their character the intermediate plates of 

 the Asterinidse, whilst their arrangement also approaches in a certain degree that of some 

 of the Pentagonasteridse. 



2. Mimaster cognatus, n. sp. (PI. XLVII. figs. 3 and 4 ; PL LXII. figs. 4 and 5). 



Pays five. R = 63-65 mm.; r = 21 - 5 mm. R=3 r. Breadth of a ray near the 

 base, between the third and fourth infero-marginal plates, 20 mm. 



General form stellato-pentagonal. Rays moderately produced, broad at the base and 

 tapering gradually to the extremity, which is slightly upturned. Abactinal area more or 

 less inflated, causing a puffy appearance over the disk and an irregular subcylindrical form 

 to the rays. Actinal area subplane, but with a tendency to become convex along the ray. 

 Interbrachial arcs wide and subacute. 



The abactinal area is covered with a great number of small paxillse, which show an 

 obliquely transverse arrangement at the sides of the ray, especially distinct near the base, 

 but are irregular in their disposition in the central region of the disk, along the median 

 line of the ray, and at the extremity. The regularly disposed paxillae are larger than the 

 others, and all gradually diminish in size as they approach the extremity of the ray, where 

 they become almost microscopic. The paxillse consist of a delicate pedicle, which expands 

 considerably at the distal extremity, and is surmounted by a crown of numerous delicate 

 spinelets, which radiate more or less, and produce a tufted form of paxilla. The papulae 

 are comparatively large. 



The marginal plates are small and confined to the lateral and actinal surfaces. The 

 supero-marginal series are inconspicuous and scarcely distinguishable from the paxillas of 

 the abactinal area ; in fact, they are unnoticeable when the starfish is viewed from above. 

 The infero-marginal plates, which are about thirty-six in number, counting from the median 

 interradial line to the extremity, are comparatively large and well developed, forming a 



