AMl'IllLKlDAE 



295 



slight elevation, the more distinct as its colour is lighter than the general colour of the 

 plate. Adoral plates not prolonged outwards so as to separate the first lateral plate from 

 the buccal shield. The jaws are rather elongate. The mouth papillae are four (five) on 

 each side; the outermost one is small, scale-like, the two following ones long and 

 pointed, spine-like ; the infradental papillae are small, sometimes somewhat irregular ; 

 also the papilla of the first mouth tentacle may be double. 



The first ventral plate is small, with somewhat rounded distal edge; the following 

 ventral plates slightly contiguous, somewhat broader than long, with lightly convex 

 outer edge; the outer corners rather sharp. Dorsal arm plates broader than long, 

 biconvex. Arm spines four, slender, conical, pointed, smooth. Tentacle scales typically 

 two, but the one along the ventral plate often much smaller than the outer scale or 

 totally lacking. Colour in alcohol dark grey. 



Fig. 26. Amphioplus acutus, n.sp. Part of oral side (a) and dorsal side (h). Madreporite (c). X12. 



One specimen, St. 181, has only four rays. 



The species has separate sexes and is not viviparous. 



In the elongate, pointed mouth papillae this species differs conspicuously from 

 the other Antarctic species of Amphioplus (or A)?iphiodia). The same character is found 

 in Amphioplus gastracanthus (Liitken and Mortensen) and A. notacanthiis (Liitken and 

 Mortensen) (Ophiuroidea of the Albatross Expedition, 1891, pi. xiii, figs. 4, 7) ; but these 

 species are in other respects so different from the present species that there is hardly any 

 close affinity between them. In A. dispor (Koehler) ('Investigator' Ophiuroidea, i, 

 pi. x, fig. 81) one of the distal mouth papillae is long and spiniform; but this species 

 otherwise has no resemblance to the present species. 



To this species I must refer also some young specimens, up to 2-5 mm. diameter of 

 disk, from St. 182. They differ conspicuously from the typical adult Amphioplus acutus 

 in having only a single (but slender, spiniform) outer mouth papilla, and in having only 

 three arm spines (exceptionally a joint here and there may have four spines). Otherwise 



