262 



ASTERIAS ACUTISPINA (nOV. Sp.) 



Closely allied to .4. tenuispina Lam., and has probably been con- 

 founded with it. Kays rather short and swollen, and somewhat tri- 

 gonal from the prominence of the median dorsal ridge. A few pedi- 

 cellarite on the interambulacral plates in the ambulacra! furrows. 

 The ambulacral spines are frequently arranged in two rows on the 

 inner half of the ray, with two spines (at intervals only one) to each 

 interambulacral plate. Sometimes there will be two rows on one 

 side of the furrow, and only one on the other, — an irregularity 

 resulting from the heteractinic development of the species. These 

 spines are flattened, linear, and truncate at the extremity, rarely 

 showing any concavity or groove near the extremity, which con- 

 stantly occurs in A. tenuispina. Ventral spines rather stout, some- 

 what compressed, tapering, but scarcely acute, a little longer than 

 the ambulacral spines, and forming two or three longitudinal series, 

 according to the distance from the disc ; those of each transverse row 

 connected at base, as usual; those of the outermost series have a 

 half-crown of minor pedicellariae * at about the middle on their outer 

 sides. The dorsal spines are acute, subconical, slender, with wreaths 

 of minor pedicellariae near their bases, and are arranged, as in the 

 other species of the group, in five rows. In the marginal rows there 

 is about one to each alternate ossicle. In the median row, which is 

 regular, the spines are rather larger and more numerous than in the 

 intermediate rows. There are a few elongated major pedicellariae, 

 variable in size, scattered between the dorsal spines. On the disc 

 there is generally one pretty large interval between the ossicles, 

 which is excentric in position. 



Of this species there are four sj)ecimens in the Museum of the 

 Smithsonian Institution. They vary In diameter from three to five 

 inches. Theii' individual character is shown in the following table : 



In specimen c the madreporic plates are confluent in two groups, 

 placed on the same side of the disc, and separated only by the space 

 occupied by two rays. 



* The pedicellariae afford excellent specific characters in the true Starfishes. In 

 the Pycnopodifhe two kinds may be distinguished. Those which we term major 

 pedicellariaj are generally sessile, and of large size, with valves either compressed 

 or apprcssed. Those of the other kind, wliich we call minor pedicellariae, are 

 always minute and pedunculated, the pedicels often brandling, and the valves 

 oblong, thick, and blunt. The Wreaths around the bases of the dorsal spines are 

 always formed of the latter kind. 



