422 THE VOYAGE OF H.M.S. CHALLENGER. 



conical spinelet, and on the surface of the plate a few small, equal, isolated, widely spaced, 

 miliary spinelets. The basal plates are also similarly armed with a central conical spinelet 

 and a few widely spaced miliary spinelets. The under-basals only bear miliary spinelets, 

 and a few are present on the flanks of the dorso-central plate. 



The supero-marginal plates, about twenty in number from the median interradial line 

 to the extremity, are large and narrowed abactinally (at least at the base of the ray), 

 leaving small angular spaces in which the papular orifices are found. Each plate bears 

 one large central spinelet and several smaller ones. The infero-marginal plates are much 

 smaller than the supero-marginal series, diminish rapidly in size as they proceed along 

 the ray, and do not reach the end of the ray, the adambulaeral plates being there con- 

 tingent on the supero-marginal series. Each plate, before they become very small, bears 

 a large conical spinelet and two or three smaller ones. 



The adambulaeral plates are small, rather broader than long, and with an angular 

 prominence into the furrow ; all the plates being equally prominent into the furrow. 

 Their armature consists of a transverse series of three cylindrical tapering spinelets, nearly 

 as large as the largest spinelet on the marginal plates. The innermost spinelet, which is 

 rather smaller than the other two, stands at the apex of the angular prominence and is 

 directed over the furrow, the other two are equidistantly spaced on the actinal surface of 

 the plate and radiate slightly apart. The median spinelet is usually slightly the longest. 

 About seven adambulaeral plates are included within the wide actinal groove of the 

 terminal plate. 



The mouth-plates trend upward towards the buccal cavity, and they bear on their 

 surface two large robust actinal spines. The actinostome is large. 



I have found no trace of any actinal intermediate plates between the infero-marginal 

 and the adambulaeral plates. 



The madreporiform body is small and very difficult to see. It is situated between 

 the basal plate and the innermost pair of supero-marginal plates, and is consequently quite 

 at the edge of the disk. Its surface is traversed by what may be described as three or 

 four very coarse ridges rather than striations, and it is essentially embryonic in character. 

 The anal aperture, which is large and excentric in position, is situated between the 

 dorso-central and basal plate, the margin of the former being deeply lunated for its 

 reception. Several papilliform spinelets surround the orifice. 



The ambulacral tube-feet, which are arranged in two simple and regular rows, have 

 fleshy terminal knob-like disks, which appear to be capable of invagination. 



The terminal plate is very large and deeply indented adcentrally for the reception of 

 the termination of the median radial series of plates. It bears three large spinelets on 

 each side near the extremity, and there appears to be a prominence in the median line 

 abactinally on which a spine was probably originally borne. In addition to these, isolated 

 miliary spinelets are also present on the surface. 



