REPORT ON THE ECHINOIDEA. 89 



with the narrow coronal plates of a lighter violet tint forming a most regular pavement on 

 the actiiial and abactinal surfaces of the test. The interstices between the coronal plates 

 are even more developed in this species than in AstJienosoma fenestratum, extending 

 as they do from the edge of the poriferous zone nearly to the extremity of the coronal plate 

 in the median interambulacral space where they lap. The lapping of the plates is very 

 marked in this species, even when seen from the outside (PL XIX.'' fig. 2). The lapping 

 of the ambulacral plates is not so well marked except in the older plates towards the 

 ambitus on the abactinal surface. The encroachment of the interambulacral plates on 

 the outer edge of the ambulacral plates is also shown from the exterior, the wnngs of the 

 extremities of the plates covering the ends of the corresponding plates of adjoining 

 areas, as has been abeady noticed by Thomson in Asthenosoma hystrix. On the actinal 

 side this lapping is not well seen, the plates appearing externally to abut regularly 

 both in the ambulacral and interambulacral areas (PI. XIX. "^ fig. 1) as in the Desmosticha 

 proper ; but an examination of the interior of the test shows the lapping of both areas 

 to be as prominent as in the figure of Asthenosoma hystnx given by Thomson (Porcup. 

 Echin., Trans. Roy. Soc, 1874, pi. Ixv. fig. 2). The primary spines of this species are few 

 in number (PL XIX." fig. 1, PL XIX.^ figs. 1, 2), and are limited to a few plates near the 

 ambitus on the actinal and abactinal surfaces, in addition to the single prominent row 

 extending from the actinostome a short distance over the ambitus, to the abactinal region 

 (PL XIL^figs. 14, 15, PL XIX.^ fig. 1, PL XIX.^ fig. 2) along the outer edge of the inter- 

 ambulacral zone next to the poriferous zone. The other spines, secondary and miliary, are 

 also few in number, and slender, and are irregularly arranged on the ambulacral and inter- 

 ambulacral plates ; there are a number of miliary tubercles forcing then- way through the 

 cuticle, which appear as pits (PL XII.'' figs. 14, 15). The gUls in this species are large 

 and prominent (PL XIX." fig. 1). Judging from the single alcoholic specimen the 

 ambulacral tentacles of this species must have been of an unusual size (PL XIX." fig. 1, 

 PL XIX.'^), especially near the ambitus l^oth on the actinal and abactinal surfaces. The 

 sucking disks are not large even on the actinal sm'face, and on the abactinal surface they 

 soon become, beyond the ambitus, more slender and pointed (PL XIX.'' fig. 4). The al^ac- 

 tinal system is comparatively smaller than in Asthenosoma coriaceum, and diflfers mainly 

 in the position of the genital openings which are relatively more distant from the centre 

 than in Asthenosoma coriaceum ; the tuberculation of the anal system is also coarser in 

 the latter species and is covered by larger plates. Compare Plate XIX.'' fig. 3, and Plate 

 XVII.^ fig. 5. 



Station 204. November 2, 1874. Lat. 12° 43' N., long. 122' 10' E.; 100 fathoms 

 and 115 fathoms ; mud. 



* Asthenosotna gracile, n.sp. (PL XVII.* figs. 1-4). 



This species resembles Asthenosoma hystrix in having comparatively narrow elongated 



(ZOOL. CHALL. EXP. — PART I.X. 1881) I 12 



