36 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 8 



slightly tapering. Three uniform short arm spines on next 2 arm seg- 

 ments, blunt and uniformly tapering. Two very short and peglike arm 

 spines on the remaining arm segments. 



Oral shields diamond shaped, longer than broad. Adoral plates dia- 

 mond shaped, slightly broader than long, meeting fully within. Jaws 

 quadrilateral, longer than broad. Four oral papillae, broad and blocklike, 

 broader than long, their outlines cannot be seen distinctly. 



Interbrachial spaces below covered by 2 long, narrow plates, distal of 

 the oral shields, and separated at the disk margin by a triangular plate, 

 the acute angle within and a broadly rounded margin without that ex- 

 tends beyond the disk margin, appearing much like a horizontal keel on 

 the large interbrachial plate. Genital slits not visible. First under arm 

 plate large, shield shaped, succeeding plates similar but becoming smaller 

 distally, disappearing entirely on the 6th arm segment. Under plates 

 widely separated by the side arm plates. Tentacle scales only on the 

 basal 5 arm segments, 2, sometimes 3, small oval tentacle scales on each 

 pore. 



Color. — All specimens dried from alcohol are bleached nearly white. 



Types. — Holotype, AHF no. 16; 3 paratypes, one in M.C.Z. 



Type locality. — Station 810-38, 73 fms., off Barrington Island, Gala- 

 pagos, January 26, 1938. Paratypes: one from Station 767-38, 45 fms., 

 off Chacahua Bay, Oaxaca, Mexico, January 9, 1938; and 2, one in the 

 Museum of Comparative Zoology, from Station 792-38, 75 fms., off 

 Daphne Minor Island, Galapagos, January 20, 1939. 



Remarks. — This little brittle star differs markedly from other known 

 members of the genus by its smooth, flat disk with 10 marginal knobs (or 

 at least elevations) on the 5 radial and 5 interradial marginal plates. The 

 name leurum has been selected with reference to the very flattened form 

 of the entire body. 



Genus AMPHIOPHIURA Matsumoto 



Amphiophiura irregularis, new species 

 Plate 7, Figs. 4-6 



Description. — Disk diameter, 7 mm.; vertical diameter, 1.3 mm.; 

 arms, 18 mm. long. Disk pentagonal, flat, composed of 24 flat plates, 

 including the radial shields; 8 irregular plates surround the central plate, 

 a large oblong interradial plate separates the radial shields. The number 

 of disk plates ranges from 20 to 26, including radial shields, in the 16 



