A Revised List of British Echinoidea. 407 



Diagnosis. 

 The test is of extreme tenuity ; the primary ambulacral plates 

 are fully as high as the corresponding interambulacral plates ; 

 there is but little difference between the upper and lower surfaces 

 of the test. " The large tubercles are not closely packed, but 

 irregularly arranged and limited to a comparatively narrow edge 

 of the abactinal surface, immediately adjoining the ambitus" 

 (Agassiz, 3,^1. 103). 



Distribution 



British Seas. — N.-W. of Lewis, warm area, " Knight Errant," 

 St. 4, 555 fms. (Agassiz, 4). 



Other Localities. — Off Cape St Yincent, " Challenger," St. YL, 

 1525 fms. Off the Azores, St. 78, 1000 fms. (Agassiz, 3). Coast 

 of U.S.A., 568-1080 fms. (Yerrill). Lesser Antilles, 399-1224 

 fms. (Agassiz, 5). 



3. Asthenosoma, Grube. 



1867. Asthenosoma, Grube, Jaln-esb. Schles. Ges. vaterl. Cult., p. 42. 

 1870. Calveria, Wyv. Thomson, in Carpenter, etc., Rep. "Porcupine" 

 Exp., Pi'oc. Roy. Soc, xviii., p. 445. 



Test flexible, depressed ; ambulacral and interambulacral areas 

 composed of narrow plates, which are expanded and overlap 

 extensively ; oral and apical surfaces of test not different in 

 character ', calcareous deposit limited to centre of plates, which 

 are thus membranous at the edges ; each area has a principal 

 vertical row of large perforate tubercles ; rest of plate occupied 

 by similar smaller tubercles in an irregular horizontal line. 



5. Asthenosoma hystrix (Wyville Thomson), Agassiz. 



1870. Calveria hystrix, Wyv. Thomson, in Carpenter, etc., Rep. 



" Porcupine" Exp., Proc. Roy. Soc, xviii., 

 p. 445. 

 1872. Athenosoma hystrix, Agassiz, Rev. Echin,, pp. 93, 273, pi. iic, 



figs. 1-5. 

 1874. Calveria hystrix, Wyv. Thomson, *' Porcupine" Echin,, Pliil. 



Trans., p. 738, pis. Ixiv., Ixv. 

 1883. ,, ,, Agassiz, "Blake" Echin., Mem. Mus. Comp. 



Zool., x., p. 29, pis. xiii., xiv. 



Diagnosis. 



The characters distinguishing this species from the only other 

 known British form are given below. I have only seen specimens 

 of the present one. 



