278 VERRILL 



PTERASTERIDES APORUS (Ludwig) Verrill. 



Pteraster aporus Ludwig, Zool. Jahrb., p. 293. 



Plerasterides aporus Verrill, Amer. Naturalist, XLiii. p. 547, 1909. 



I have not seen this species. The original description follows : 

 " The radius of the disk is 35 mm., that of the arm, 98 mm. 

 Where the arms branch off from the disk, the width is from 40 mm. 

 to 42 mm. Both disk and arms are somewhat flattened. The supra- 

 dorsal membrane is rather thick, soft, with corrugated (wrinkled) 

 upper surface, through which calcareous spines in no wise protrude ; 

 in its outermost layer are found, on microscopic investigation, 

 numerous reticulate little calcareous bodies, from the outer surface 

 of which small pointed spinelets project. The paxillse, which support 

 the supradorsal membrane, consist of a pedicel (stalk) from 2 mm. 

 to 3 mm. long, from the upper end of which, as a rule, four much 

 thinner spines, about 5 mm. long, diverge. On the inner dorsal skin 

 the paxillae are inserted at intervals of 3 mm., on the average. The 

 calcareous net of the inner dorsal skin, on the knotted points of 

 which the paxillae stand, is made up of more or less elongated calca- 

 reous plates, which partly overlap the knotted points of the network, 

 like tiles. In the circtunference next to the large anal opening into 

 the nidamental cavity are some noteworthy thick paxillae, which bear 

 on their upper ends a great number of spines. On the under side of 

 these starfishes one may count, on each arm, over fifty pairs of little 

 feet and a corresponding number of fins (or combs). Towards the 

 exterior the overlying marginal border is so wide that it reaches to 

 the edge of the arms. All the spines of the marginal border and of 

 the combs are enveloped for their length in a rather thick and soft 

 membrane. In each comb lie from eight to nine spines, of which the 

 two innermost, standing next to the ambulacral furrow, are very 

 weak and much shorter than the six to seven outer ones, which are 

 strong and of about equal size. Between the combs may be seen the 

 large segmental apertures furnished with clapper-shaped aperture- 

 papillae. At the mouth, each jaw carries an oral comb, which bears 

 six spines (' mouth-spines proper,' Sladen) and is not united with its 

 neighbor. Towards the exterior from this comb, on each jaw, is a 

 light, curved, rarely strong, single spine ('secondary mouth-spine,' 

 Sladen) which likewise is covered by the soft skin. 



" From all the species of Pteraster now known (militaris Miiller 

 and Troschel, pulvillus M. Sars, multipes M. Sars, capensis Gray, 

 cribrosus v. Mart., dance Verrill, affinis Smith, rugatus Sladen, 

 stcllifer Sladen, scmireticulatus Sladen, carribceus Perrier). the 



