EASTERN TROPICAL PACIFIC ASTEROIDEA. 89 



says, that the iiuu-nnost oral should be considered a suboral but I have not the 

 material to determine the point. In using the following key to the species of 

 Hymenaster, these possible variations in number of adambulacral, oral, and 

 suboral spines must be kept in mind and when there is any doubt both alterna- 

 tives should be followed out. The key includes not only all the species listed 

 above, but also the two new forms described below, each of which has some 

 very distincti\'e characters. Of cotu-se the accumulation of more material will 

 bring out defects in the present key, but it will serve as a begimiing for a satis- 

 factory brief expression of the taxonomy of the genus. It will be noticed that 

 some of the characters which were considered of primary importance by Sladen, 

 such as the reticulation of the supradorsal membrane, and the body-form, are 

 here either ignored entirely or relegated to a very subordinate position. This 

 has been done because these characters vary so much with the condition of the 

 specimen, as to be of doubtful value. Most Hymenasters are secured only by 

 dredging or trawling in very deep water and they reach the sm-face in a more 

 or less contracted, contorted, and often damaged condition. It is therefore 

 often impossible to determine what the form and appearance in Ufe were. Since 

 the calcareous parts are less likely to be altered by capture and preservation, 

 I have sought to use these as far as possible in distinguishing the species. Proba- 

 bly this leads to a more artificial arrangement than if all the characters could be 

 considered but imder existing conditions any arrangement of the species of so 

 Ut tie-known a genus must be more or less non-phylogenetic. 



Keij to the species of Hymenaster. 



A. Adambulacral armature of one spine. 

 B. Suboral spine single. 



C. Oral spines 2 cremnodes. 



CC. Oral spines 3 or 4. 



D. Spiracula not in definite circumscribed areas, except for regular transverse bands on inter- 



braohial membrane; oral spines nearly as long as jaws nohilis. 



DD. Spiracula in definite circumscribed areas but transverse bands on interbrachial membrane 

 replaced by small, detached, scattered areas; oral spines about half as long as jaw or 



less koehleri. 



BB. Suboral spines 2 on each plate. 



C Oral spines 2 fornwsits. 



CC.i Oral spines 3 or 4. 



D.i Actinolateral membrane thin with very long actinolateral spines; spiracula very small 



in widely scattered groups of &-10 pergamentaceu.'i. 



DD.' Actinolateral membrane thick with short or moderately long actinolateral spines buried 

 in it; spiracula moderately large in irregular groups of usually more than 10. 



E. Suboral spines acicular rhxidopeplus. 



EE. Suboral spines thick, stout, sacculate violaceus. 



AA. Adambulacral armature of more than one spine. 



