662 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxn. 



present (0.095 mm.). Complete regular buttons have six holes in two 

 rows. Some specimens have more complete buttons than others. The 

 figures will show a few of the principal variations, although, as already 

 mentioned, it is difficult to duplicate an}' of the irregular patterns. 

 The pedicels have a well developed terminal plate. Near this plate 

 are numerous irregular, but more or less bilateral, fenestrated plates, 

 about 0.08 l\y 0.18 mm. The dorsal papilla? have the rudiments of a 

 terminal plate and the walls are sti'engthened by numerous slighth" 

 curved rods with short branches along the sides, often uniting to form 

 one or two holes. The tips are slightly expanded and have one or 

 two perforations, or none. Frequently the lateral branches are very 

 short and appear as spines. An average rod is about 0.35 mm. long, 

 although much shorter and slightly longer forms occur. Grotesque 

 incomplete buttons (or plates) of the large variety are present, with 

 fewer complete examples. 



According to Theel, this species is most nearly related to Holotharia 

 curiosa Ludwig. There appear to be more tables and spires in the 

 ATbatrosa material than in the type specimen of Theel, which came 

 from the "Sandwich Jslands." Considering, however, the form of 

 the buttons and color of the animals there is little doubt but that my 

 specimens are referable to Theel's species. Clark ^' has recorded this 

 form from Albemarle Island, Galapagos group, and Sluiter from 

 Paternoster Island (Siboga Holothurioidea, p. 15). 



HOLOTHURIA ARENICOLA Semper. 



Sporadipua {Acolpos) macttlatiis Brandt, Prodr., 1835, p. 46. — L.^mpert, See- 



walzen, 1885, p. 73. 

 Hololhurki, arenicola Semper, Holothnrien, 1867, p. 81, pi. xx; pi. xxx, fig. 13; 



pi. XXXV, fig. 4.— Theel, Challenger Holothurioidea, Pt. 2, 1886, p. 222. 



General form subcylindrical, elongate, ])lunt at both ends; body 

 rather slender, the ventral surface arched, but not so much so as the 

 dorsal. Mouth small, turned ventrally, the circlet of very small ten- 

 tacles surrounded by an inconspicuous collar bearing blunt papilla?. 

 Anus terminal, bordered by five angular groups of three to six short 

 papilla?. Tentacles verj' much retracted, apparently about twenty' 

 (which is the normal numl)er for this species). Am))ulacral append- 

 ages in the form of pedicels more or less scattered. The two ventral 

 ambulacra are well marked, the pedicels being larger and rather 

 closer together than on dorsal surface. A faint indication of arrange- 

 ment in series is seen. Body wall of medium thickness. Deposits: 

 Buttons and tables; the former rather regular, smooth, with six holes 

 and with the edge regularl}'^ indented between each pair of holes; the 

 latter with an annular disk with a very large central hole and a small 

 hole at base of each spire support; exceptionally with more holes; 



aProc. Wash. Acad. Sci., IV, 1902, p. 527. 



