REPORT ON THE ECHIISrOIDEA. 161 



interambulacral spaces between the broad bare ambulacral areas. The spines of the 

 actinal surface are more slender, club-shaped and hollow, while in the spines of the abac- 

 tinal region the shaft, although hollow, was quite thick. 



The secondary spines resemble the primary ones of their corresponding surfaces ; the 

 miliary spines are short and straight ; there are few small globular pedicellarise on short- 

 stems scattered round the actinostome and near the ambitus on the actinal side. Seen 

 from above the outHne is elliptical (PI. XXXII. fig. 1), truncated anteriorly, the apex 

 and apical system coincident, the apical system being slightly posterior. The test 

 arches very regularly from the apex towards both the anterior and posterior extremities 

 (PL XXXII. tig. 3) ; the actinal surface is quite flattened, the actinostome elongated, 

 (PI. XXXII. fig. 5), placed near the anterior extremity (PI. XXXII. fig. 2). 



The test is so thin that the radiating and circular canals can be seen through it round 

 the actinostome (PL XXXII. fig. 5). The anal system is placed above the actinal surface 

 in the ambitus, the subanal fasciole extending on to the actinal surface (PL XXXII. fig. 

 2). The subanal fasciole forms a horizontal line with two re-entering loops (PL XXXII. 

 fig. 4) below the circular anal system. This is covered with miliaries and short- 

 stemmed club-shaped pedicellarise. The actinostome is surrounded by a fringe of large 

 tufted tentacles (PL XXXII. fig. 5). 



Station 191. September 23, 1874. Lat. 5° 41' S., long. 134° 4' E.; 800 fathoms; 

 bottom temperature, 3 "9° C. ; mud. 



*Genicopatagus. 



Genicopatagus, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 210. 



This genus has striking afiinities with Holaster, Cardiaster, and Toxaster ; the ambu- 

 lacra, as in Toxaster are all slightly sunken, but the structure of the ambulacra is like 

 that of Cardiaster, while in outline it recalls Holaster. In the structure of the ambu- 

 lacral system of the actinostome Genicopatagus is closely related to Paleopneustes ; it 

 difi'ers from it in having the odd ambulacrum rudimentarily petaloid (PL XXXI. fig. 16) 

 like the lateral ambulacra, also in having the uniformly-sized plates composing the ambu- 

 lacra above the ambitus continued to the actinostome. A similar uniformity of structure 

 in the plates composing the interambulacral areas of the actinal and abactinal region 

 also distinguishes this genus from Paleopneustes (PL XXXV. ** figs. 1, 2). The position 

 of the anal system is similar to that of Paleopneustes ; but while having the actinostome 

 of that genus and its general facies, it has not its strongly -marked Spatangoid actinal 

 surface, having no actinal plastron, and an abactinal system, which while not discon- 

 nected is yet made up of large genital plates in striking contrast to the compact apical 

 system of Paleopneustes. 



The madreporic body covers the greater part of the right anterior genital ^ilate. In 

 this species the largest specimen examined showed only a single genital opening 



(ZOOL. CHALL. EXP. — PART IX. — 1881) I 21 



