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



Brissopsis lyrifera except by sucli indifferent characters as a somewhat more compact 

 test with a slight keel from the apex to the anal system, a closer tuberculation, and a 

 slightly sharper peripetalous fasciole ; characters which are found in specimens coming 

 from such distant localities as the coast of Norway and the western shore of Spain. The 

 great liathymetrical and geographical range of this species has already been noticed. 



Station 141. December 17, 1873. Lat. 34° 41' S., long. 18° 36' E. ; 98 fathoms; 

 bottom temperature, 9 "7° C. ; sand and gravel. 



Station 142. December 18, 1873. Lat. 35° 4' S., long. 18° 37' E. ; 150 fathoms; 

 bottom temperature, 8 "3° C. ; sand. 



Simon's Bay ; 5 to 18 fathoms. Agulhas Bank ; 150 fathoms. 



*Acrope. 



Aerope, Wy. Thomson, Proc. Roy. See, vol. xxv. p. 1\\. 



The genera Aerope and Aceste, first described by Thomson in the Voyage of the 

 Challenger (vol. ii. p. 28, fig. 99, and p. 376, figs. 95, 96), are interesting as showing the 

 passage oit]iQ Pourtalesia group to the Brissina among the Spatangoids, and the affinities 

 of those genera to such forms as Cionohrissus, Brissoj^sis, and the Schizasteridse ; while 

 having a simple circular actinostome, they have already a well-developed actinal plastron 

 and rudimentary petals at the abactinal extremity of the lateral ambulacra, while the odd 

 anterior ambulacral petal takes in Aceste an extraordinary development, and forms on the 

 abactinal surface of the test a long broad sunken petaloid ambulacrum (as deeply sunken 

 as in Sdiizaster) occupying nearly the whole of the abactinal surface. The peripetalous 

 fasciole- is quite similar in shape to that of young specimens oi Brissopsis and Hemiastcr, 

 in which the petals are also reduced much to the same condition as we find them in these 

 genera, simply double rows of pores on each side of the median line within the rudimentary 

 peripetalous fasciole ; one of these genera, Aerope, retaining something of the cylindrical 

 shape of the Pourtalesise. On the other hand the Pourtalesise, through such genera as 

 PalcBotropus, Genicopatagus, and Ilomolainpas, pass to the Spatangina, and through such 

 types as Urechinus and Cystechinus to the Galeritidge and Echinolampada3. 



The striking resemblance of the young Brissopsis with its gigantic suckers in the odd 

 anterior ambulacrum (figured on plate xix. figs. 1, 2 of the Revision of the Echini) to the 

 full-grown Aerope, plainly shows the Brissoid affinities of the genus. 



The deeply-sunken odd anterior ambulacrum of Aceste shows the relationship of the 

 genus to Schizaster, of which it also has to a certain extent the outline when seen in 

 profile, without having any trace, however, of the petaloid lateral ambulacra of that genus; 

 the only amijulacrum with double pores being the odd anterior one. The other ambul- 

 acra within the peripetalous fasciole have only simple ambulacral pt)res, as we find in 

 Echinocardium, Breynia, and Lovenia, within the internal fasciole. The course of the 



