52 Proceedings of the Biological Society of Washington. 



These new species will be figured and further discussed in a 

 paper dealing with the fauna of the region based upon the 

 recently determined material in the U. S. National Museum, 

 where figures of such rare forms as Acanthaster ellisii (Gray) and 

 Leiaster teres Verrill, which the Museum also possesses from the 

 Gulf of California, will also be included. 



Family ASTROPECTINID^ Gray. 

 Sideriaster canaliculata new species. 



Five arms; R=64 mm.; r=19 mm.; R:r=3.4:l; width of ray at base 

 (measured from the interradial line) 22 mm.; superomarginals 45. 



General form stellate ; disk medium sized ; rays tapering evenly to a 

 blunt extremity. 



Gonads confined to the interradial portion of the disk, not extending 

 out along the rays. 



There are well developed superambulacral plates. 



The paxillse are closely placed, though not crowded, and are remark- 

 ably uniform in size, those adjacent to the superomarginals being only 

 slightly smaller than those in the radial line of the arms, and the latter 

 similarly only slightly larger than those in the center of the disk. 



A large paxilla from the radial region at the base of the arms has a 

 rather low thick stalk supporting a crown consisting of from six to ten 

 (most commonly seven, rarely more than eight) stout blunt radiating 

 spines, with frequently one or two (rarely more) additional much smaller 

 and shorter spines between them, and from one to four (most commonly 

 one or two) short stout round-tipped spines, resembling the radiating 

 spines but shorter, at the summit. The radiating spines are about as 

 long as the column of the paxilla is high. 



The large prominent exposed madreporite is situated exactly midway 

 between the center of the disk and the interbrachial margin. It is 

 circular, 3.5 mm. in diameter, and bears numerous more or less complete 

 septa extending from the periphery a greater or lesser distance toward 

 the center. It presents a most striking similarity to a coral polyp. 



Papulee, regularly six about each plate, occur uninterruptedly across 

 the arms. 



The superomarginals are short and broad; in the interbrachial arc 

 they are wedge-shaped, about half as long at tlie actinal as at the abactinal 

 end, 5 mm. wide and 1 mm. long at the well rounded abactinal border; 

 they are evenly curved, the arc of the curvature making an angle of 

 about 60° with the plane of the disk ; gradually they become more oblong 

 and increase in length to the fifth and following, which have parallel 

 sides and are noticeably larger than those in the interbrachial arc ; on 

 the arms they become more recumbent, lying mostly on the abactinal 

 surface, though still with a uniform curve from the actinal to the 

 abactinal border. 



The superomarginals bear on their outer surface usually three (some- 



