RECENT OPHIURANS. 331 



1304. 0. LYMANI Wtvtlle Thomson, 1873. Depths o£ the sea, p. 172, f. 32, 33. Koehler, 1909. 



Princesse-Alice Echinod., pi. 3, f. 4; pi. 4, f. 1 (colored). 



747 specimens. Off southwestern Ireland, 982 fms. Bay of Biscay, 1525 

 fms. South of Nova Scotia, 980-1250 fms. Off Nantucket, 1098 fms. East 

 of Nantucket, 810-1242 fms. South of Marthas Vineyard, 466-1241 fms. Off 

 New Jersey, 1394 fms. Off Delaware, 740-1186 fms. Off Cape Hatteras, 898 

 fms. Off South Carolina, 464-647 fms. Off Georgia, 1047 fms. Lower Cali- 

 fornia: off Point San Tomas, 1090 fms.; off Rosario Bay, 879 fms. Mexico: 

 off Mazatlan, 995 fms. Gulf of Panama, 978-1067 fms. Japan: off Shio 

 Misaki Light, 544-587 fms.; off Omai Saki Light, 624-662 fms.; off east coast, 

 535 fms. Dutch East Indies: off Aru Islands, 800 fms. 



1305. O. MONOPLAX, sp. nov. (noi/os, single + ;rXaJ, plate). Plate 20, f. 9, 10. 



Disk 12 mm. in diameter; arms about 35 mm. long. Very similar to 0. 

 serratum but differing constantly in the following characters. There is no trace 

 of an arm-comb nor of granules at the base of the arm, near the radial shields, 

 such as occur in serratum. The upper arm-plates are triangular, of moderate 

 size, wider than long (ox- at least not narrower), while in serratum they rapidly 

 become very small and are decidedly longer than wide. The under arm-plates 

 are also different in the two species; in both, the first is very small, the second 

 is largest of all, while the third and fourth are not much smaller; but in serratum 

 the fifth is somewhat smaller than the fourth though not of very different shape 

 and the succeeding plates decrease in size rapidly but remain distinctly wider 

 than long and are not triangular; while in monoplax, the fifth is markedly smaller 

 than the fourth and of different shape, being distinctly triangular as are the 

 succeeding plates which steadily diminish in size. In serratum there are half 

 a dozen low, wide oral papillae, while the point of the jaw bears the lowest tooth; 

 in monoplax, there are 7-9 papillae, the proximal all pointed, and a pair of them 

 occupy the tip of the jaw. Instead of 4-6 sharp, unequal arm-spines, character- 

 istic of serratum, there are 6 or 7 blunt, equal spines in monoplax, shorter than 

 those of its near relative. Finally, in monoplax each of the six tentacle-pores 

 (three pairs) is covered almost wholly by a single large oral tentacle-scale (hence 

 the name), attached to the side arm-plate. In his description of serratum, 

 Lyman says there is "a single, circular tentacle-scale" on the "under arm 

 plates," but the figure in the Challengkr report (Plate 2, f. 1) shows clearly 

 the real condition in that species, one or two low imperfect scales on both the 

 under and the side arm-plates. Color (dry), nearly white. 



HoLOTYPE (M. C. Z. 508) and 14 paratypes (M. C. Z. 509-516, 882). 



