NO. 1.5,%. HAWAIIAN HOLOTHURIANS— FISHER. 687 



Externally the species is practically indisting-uishable from the fore- 

 going. Some specimens of jxirvci have apparently fewer pedicels on 

 themidventral region, and less diversity, especially in small individuals, 

 in size of dorsal pedicels. The species can always be readil}^ separated, 

 however, on the character of the tables. It will be noticed \\\^t jjai'va 

 lives on a hard bottom and luurrayl on a soft. Just how much signi- 

 ficance this fact has in accounting for differences in the structure of 

 the calcareous deposits it is impossible to say. These two species exem- 

 plify very well one of the difBculties which constantly besets a system- 

 atist. Taking the specimens as a whole, two views are possible con- 

 cerning them: (1) That the two forms represent one variable species; 

 (2) that the two forms are specifically distinct. In the present case, 

 (1) have we one variable species which differs widely according to the 

 nature of its particular environment, whether it be soft, oozy mud, or 

 hard sand and shells; or (2) have Ave two closely related but distinct 

 species, each dwelling on a different sort of bottom? I have followed 

 the latter view, since there appear to be no intermediate forms, and 

 since I have no difiiculty in separating the species, upon an examina- 

 tion of deposits. That the forms are very close is manifest; but it is a 

 well-known fact, not generally appreciated, that all species are not 

 necessarily separated from their nearest congeners by the same degree 

 of difference. In the present case the question also arises as to whether 

 these two species are to be identified with already known but distantly 

 dwelling forms, or are to be regarded as new but closely allied kinds. 

 Since this has to be decided by literature and not specimens I have 

 chosen the more conservative course, although it may not be the 

 correct one. 



Mesothuria parva was taken by the Challenger in 150 fathoms, coral 

 mud, near Admiralty Island. 



Genus 3ATHYPLOTES Ostergren. 



Bathyplotes Ostergrex, Zur Kenntnis.s der Subfamilie Synallactinae unter den 

 Aspidochiroten, Zoologiska Studier, Festsch., Wilhelm Lilljeborg, 1896, 

 p. 351. Type, Stichopus natans Sars. 



Mouth ventral to subventral, anus subdorsal to nearly terminal. 

 Ventral surface more or less flattened, with the rows of pedicels on 

 all three or only on the two lateral ambulacra. Dorsal surface arched 

 with a double row of papillse along each radius, and often besides with 

 small papillae scattered sparingly over the interradii. Dorsal papillfe 

 sometimes very irregular in distribution and a ventral-lateral series in 

 addition to pedicels sometimes present. Tentacles 15 to 20. Gonad 

 in two tufts (a right and a left). Longitudinal muscles undivided. 

 Calcareous deposits: Tables with usually a four (three to eight) armed 

 disk, bearing a spire of an equal number of rods; C-shaped spicules 

 usually present. 



Proc. N. M. vol. xxxii— 07 44 



