188-1.] SPECIES OF OREASTKR. 85 



valvular pedieellarise are, on the other hand, pretty numerous, and 

 are especially rich along the sides of the ambulacra. The marginal 

 plates are very regularly granulated, and small valvular pedicellariae 

 are not unfrequently developed. The granulation on the Upper 

 surface is more delicate. The pore-arese are very regular, triangular, 

 and of moderate size ; at the nodal points spines or spinous tubercles 

 are always developed ; and we have here one of the rare cases of 

 the development of dorsal without ventral spiues. 



Colour (dry) more or less white. 



Measurements : — 



Hub. China (Swatow). 



Oreaster troscheli, sp. uov. 



A triplacanthid form, most nearly allied to 0. or lent alts, but dis- 

 tinguished from it by the following characters: — There are not more 

 than three spines in the second row of adambulacral spines on each 

 plate ; the spines are, as a rule, developed only on the distal mar- 

 ginal plates, and those that do not carry spines bear a number of 

 valvular pedieellarise. 



R=3 r. Disk not elevated ; arms distinct, not wide at their base, 

 and tapering very gradually. A median dorsal row of fairly well- 

 developed spines ; the five apical spines very strong ; most of the 

 angles of the poriferous areae on the disk are provided with spines ; 

 there are no spines on the ventral plates. 



About 25 superomarginal and 27 inferomarginal plates ; the latter 

 are confined to the abactinal aspect, save at the end of the arm. 

 The superomarginals are very high in the angles, but are shorter 

 along the sides of the arms ; in exceptional cases a spine or two 

 may be developed on them in the proximal, but, as a rule, they 

 are confined to the distal half of the arm. They are often well 

 developed sharp processes. Owing to the position of the terminal 

 superomarginals, the two last spines are set quite on the abactinal 

 surface. The spines on the inferomarginals are rare and small ; 

 but these, as well as the non-spinose superomarginals, are richly 

 provided with pedicellariae. 



Adambulacral spines in three rows ; the innermost delicate, short, 

 about ten in number; in the middle row there are two or three stout 

 spines, and in the outermost two or three, not quite so regularly 

 developed as the rest. The immediate buccal armature is formed by 

 the elongation and strengthening of the spines of the lowest row. 

 The ventral ossicles are (airly distinct from one another, and are very 

 richly provided with pedicellariae. A considerable number of pedi- 

 cellariae are likewise developed on the abactinal aspect of the disk and 

 arms ; like all those in this species, they arc sessile and valvular. 



The pore-ureae are large and numerous, so that the reticulation ot 



' Shrunk in d\ inc. 



