RHINOBRISSUS Ml< aASTEBOIDES 67 



fasciole is broad, elliptical, and the greater part of the space it encloses is 

 filled by the huge suckers of the odd anterior ambulacrum. The close 

 resemblance of this stage of Bemiaster to an Aerope is very marked, and 

 the permanence of the unusual developmeni of the tentacles of tin- odd 

 anterior ambulacrum up to the adult stage is an important link in tracing 

 the affinities of such widel) separated genera as Bemiaster, Brissopsis, A 

 Bizia, Aerope, Aceste, and Schizaster. 



The structure of the larger interambulacral spines in the young stages 

 (7 mm. long, diameter) well shows the manner in which the fantastic shape 

 of some of the Spatangoid spines is produced. The outer sheath of calcareous 

 rods lie. -nine- solidified as thin lamellae, forming in one ease in the primary 

 interambulacral spines of the anterior part of the tesl on the abactinal side, 

 above the ambitus, a spearlike head to the shaft of the radioles; this may 

 have a more or less lobed edge, or if the radiole i- curved it forms a some- 

 what shallow spoon-like extremity with spiny processes; in the shorter 

 radioles of the actinal plastron the lamellae all develop into this spoon-shaped 

 extremity, which may he perfectly symmetrical or else developed une- 

 qually on one side, according to the position of the radioles on the actinal 

 plasl ron. 



In the earlier stages the fasciole- are already covered bj the same kind 

 of pavement which we find in the adult, made up of short-stemmed, club- 

 shaped Bpines closely packed together. There were in some of the larger 

 specimens a few large, short-stemmed, globular pedicellarise, irregularly scat- 

 tered over the abactinal surface of the test. 



Rhinobrissus micrasteroidcs A. Ao. 



Rhinobrissus micrasteroidea A. A.G. Bull. M. < ' /. . V , No. 9, p. 192, 1878. 

 Off Havana, IT", fathoms. 

 Station 321, Lai 32 ' 43' 25" M oms. 



PI. XXIII. Figs. /-;. PI. XXVI. Fig. >,. 



li is with considerable hesitation that this species is retained in the 

 genus Rhinobrissus, the only specimen obtained by the Blake being a 

 somewhat damaged young stage. From what is known of the modifica- 

 tion of the Spatangoids due to growth, there are no characters in this 

 Bingle specimen which are not probably merely modifications due to age. 

 The ambulacra are all flush with the test, and remind us of the earliest 



