RETORT ON TIIE ASTEROIDEA. 57 



group, which in posture fancifully resembles the hand when held slightly hollowed as if to 

 catch a ball. (2.) A single, conical, tapering, sharply pointed spine, nearly as long as the 

 short lateral spines, stands on the actinal surface of the plate. There are also on the 

 surface of the plate two or three very small spinelets or thornlets on both sides of this central 

 spine placed at each end of the plate, in such a way as to appear to form a continuation 

 of the marginal series above described ; and there may be one or two small spinelets, equal 

 in size to these lateral ones, or a trifle larger, near the base of the central spine. Beyond 

 these there are no other spinelets on the adambulacral plates. The scoop-like groups of 

 the marginal series extend over the furrow, and touch the corresponding groups of the 

 opposite side, widely separating the pairs of ambulacral tube-feet. 



The mouth-plates are comparatively large and broad, and the united pair are con- 

 spicuous in consequence of their subtubercular character, and of a well-defined depression 

 at the outer extremity of the pair, in which no plate is present between them and the 

 marginal plates. The free margin of the united pair is well rounded and more tumid 

 laterally than a semicircle ; its armature consists of six spinelets for each plate, the inner 

 one being twice as large as the others, which are nearly equal in length ; there is thus a pair 

 of prominent but short spinelets at each mouth-angle directed horizontally over the buccal 

 membrane, whilst the remaining five mouth-spines of each plate maintain in their posture 

 more or less of the scoop-like character of the adambulacral armature. On the actinal 

 surface of the plates there is one secondary mouth-spine similar in character to, but 

 scarcely as large as, the actinal spines on the adambulacral plates ; a lineal series of about 

 six small, uniform, thorn-like spinelets runs parallel to the median suture ; and three or 

 four similar spinelets also form a lineal series behind the secondary mouth-spine. 



No actinal intermediate (ventral) plates of any kind are present ; and the marginal 

 plates are contingent on the adambulacral plates throughout. The ambulacral tube-feet 

 have a small, but definite and rounded, knob-like tip. 



One large, compound pedicellarian apparatus is situated in each interradium, placed 

 between the two innermost infero-marginal plates. It is of oval form, with the length 

 about equal to half the breadth of the marginal plates, and its margin is beset with ten to 

 twelve small pointed spinelets directed horizontally from the two sides in order to close 

 over a central cavity. This organ is placed close to the inner margin of the marginal 

 plates, and encroaches equally upon each of the two plates. A similar pedicellarian 

 apparatus occurs in the lateral vertical wall of three of the interbrachial arcs, situated 

 between the two innermost supero-marginal plates. No other pedicellariae are present. 



The anal aperture is subcentral and very distinct ; and the spinelets of the surrounding 

 paxilla), which form its margin and close over the aperture, are sensibly more robust than 

 any of the others. 



The papulae are confined to a small group, which forms a definite papularium at the 

 base of each ray, and there are not more than six papulas in each, and sometimes only 



(ZOOL. CDALL. EXP. PART LI. 1887.) 8 



