from J^iKin atul Ow Indian Ocoan. 85 



narrow, p^cneially with ft series of holes in the meJian line ot' 

 the covor-plate. 



SphaM-idiaj are found on both sides, wnnliii<; only on the 

 Iwo or ihrco ))l;«fi's nearest to the aj)ical area. Tnt>y do not 

 .|)re.'-ent peculiar features. 



The s|)icules (PI. V. fi;;:. 11) of the actinal luh' feet are 

 rather lar<;e, irici;nlar, thorny, fenestrated plates, arrani^cd iu 

 four longitudinal series. The sucking-disk is well developed. 

 'J'he abactinal tube-feet are h\rge and prominent, uiih neither 

 suckiiifj-disk nor spicules. 



'J'he test is of a faint flesh-colour ("incarn:itiis"j *, in two. 

 of the sj)eeinious ralher pale. The si)ines of t!ie ahactinal 

 side are greenish, those of the actinal side whitish; they aie 

 iK-t ringed. 



In my woik on the 'Ingolf' I'^chinoidea 1 stated f that 

 the tetradactylous jiedicellariai must probal)ly be derived from 

 the tiidentale ones ; de Meijere (' Sibo^a' Eehinordea, p. 35) 

 thitdis it more ])robable that they are derived from tlie 

 ophicephalous form. It does not seem to me very probable 

 that they be developed from either of these forms. Tliere i-*, 

 indeed, nothing in the structure of the tetradactylous pedi- 

 cellaria3 which points in either direction, and I do not see 

 why they cannot represent a special form of pedicellarit«, 

 dcvelo[)ed independently of the other forms. V>j their 

 glands (such are evidently also found in the most developed 

 forms, \\\(i%^ oi A. feneslralam •A\\<\coriaceuni) they remind us 

 of the globiferous ])edicellaria3 in other regular Eehinids, and 

 they must certainly be regarded as analo^^ous, if not homolo- 

 gous, with the globiferous pedicellarite. The form of pedi- 

 cellaria in llapalosoma described by me in the 'Ingolf* 

 Kchinoidea (p. 55) as a primitive globiferous pedicellaria, 

 not seeing its relation to the tetradactylous pedicellariaj, 

 cannot, of course, any longer be regarded as a primitive form, 

 now that the three- valved "tetradactylous" pedicellarise of 

 A. tesstllatum and A. Owsteni have been made known. As 

 rightly pointed out by dc Meijere, it must be regarded as a 

 case of extreme develo])ment, in which the valves have become 

 rudimentary and the glands excessively developed. 



T'hc foim of these curious tetradactylous pedicoUariaj shows 

 such gradual changes that it seems reasonable to regard 

 A, Owshhi as the most primitive of the species of Armosoma ; 

 the tact that the largest form of tridcutate pedicellaria; is 



• Snccnrdo, 'Chromotaxia,' ii. ed. (1804). 



t According to de Meijer*'. I am unable to find tho place where the 

 elatciuont occur.-, Lul I dnrv uot deny thai I roalh made it. 



