KEPOET ON THE ASTEKOIDEA. 5 



Genital foramina opening upon the abactinal surface close to the marginal plates on 

 each side of the odd interradial plate. 



Remarks. — The genus Benthopecten, recently described by Verrill, 1 is stated to be fur- 

 nished with abactinal plates covered with skin, usually bearing a single spine or sometimes two 

 or three, but not forming true paxillas. This character would seem to indicate an alliance 

 with Par'archaster ; but from the brevity of the description I cannot say whether this be 

 near or remote, and I am for the same reason unable to indicate in the foregoing synoptic 

 table the relative position of the genus in the family. No mention is made of the presence 

 of any odd interbrachial marginal plate and spine, or of the limitation of the papulae to 

 the basal region of the rays, — characters which are so conspicuous in Pararchaster, and 

 whose importance from a structural point of view could scarcely have been overlooked by a 

 naturalist so well acquainted with starfish anatomy as Professor Verrill, had they been 

 present in Benthopecten. Furthermore, no mention is made of the presence of any pedi- 

 cellarian apparatus. On the other hand it is recorded that " a circle of four to six papillae, 

 placed singly, surrounds each plate." If the word " papillae" here stands for the organs 

 which I call papula (following Stimpson), it would appear extremely doubtful whether 

 Benthopecten would find a place even in the same subfamily as Pararchaster. 



The subjoined scheme will assist in the ready recognition of the different species of the 

 genus. 



Synopsis of the Species included in the Genus Pararchaster herein described. 



A. No pedicellarise of any kind. Single spinelets on the abactinal plates. 



a. Abactinal area of disk plane. One supero-marginal spine. Adarnbulaeral 



plates with two actinal spines. No line of thornlets on the infero-niar- 



ginal plates ........... semisquamatus. 



b. Abactinal area of disk inflated. Two supero-marginal spines. Adambulacral 



plates with three actinal spines. A line of thornlets on the infero-mar- 



ginal plates ........... antarcticus, 



B. With special comb-formed pedicellarise. Abactinal plates with one to three or 



more spinelets. 



a. With pedicellarias between each infero-marginal plate ... . pedieifer. 



b. With no pedicellarise between the infero-marginal plates. 



a. One lateral spine on infero-marginal plates and a small companion. 



Adambulacral plates with sis or seven furrow spines, one 

 actinal and sometimes a small companion behind it. Abac- 

 tinal plates with one or two spinelets, all simple. Comb-like 

 pedicellarise on the abactinal surface .... armatus, 



b. Three or four lateral spines on infero-marginal plates. Adambulacral 



plates with four furrow spines, and two actinal side by side. 

 Abactinal plates with several long needle-like spinelets inter- 

 spersed amongst the simple ones. No comb-formed pedicel- 

 larise on the abactinal surface ....... spinosissimus. 



1 Amer. Journ. Set. and Arts, Sept. 1884, vol. xxviii. p. 218. 



