112 the apodous holothueians 



Rhabdomolgus ruber. 

 Rhabdomolgus ruber Keferstein, 1862, p. 34 ; pi. xi, fig. 30. 



Length. — 5 mm. with diameter of .6 man. (preserved material). 



Color. — Briglit red or carmine. 



Distribution. — Reported from St. Vaast (Keferstein) and "Sudspitze von 

 Helgoland" (Lndwig). 



Remarks. — Keferstein secured only a single specimen, and that was fioat- 

 ing near the surface, so that the question was raised as to whether the animal is 

 pelagic. Ludwig (:05), however, has conclusively shown that under normal 

 conditions it is a bottom form. It breeds in August; the sexes seem to be sep- 

 arate and the eggs are large. 



CHIRIDOTIN.^. Ostergren, 18985. 



Tentacles with stalk short, becoming widened distally where it bears 3-10 

 digits on each side ; the digit-bearing portion forms a sort of disc which can in 

 many cases (perhaps always?) be drawn downward in contraction, more or less 

 into the basal i^ortion of the stalk; such tentacles may be called peltato-digi- 

 tate. Cartilaginous ring wanting. Stone-canal single. Eye-spots wanting. 

 Gustatory organs seldom present. Calcareous deposits either six-spoked wheels 

 or conspicuous sigmoid or C-shaped bodies, or both, often accompanied by 

 curved or straight rods or oval miliary granules; rarely minute curved rods 

 only are present, or deposits are wholly wanting. Sexes apparently separate in 

 many species, perhaps in all. 



In the following keys and descriptions there are few terms which require 

 any explanation, for nearly all are of the kind which carry their own meaning. 

 The term "sigmoid" bodies is used for curved rods which bear a more or less 

 close resemblance to that form of the Greek letter sigma, which is used at the 

 termination of a word ; that is to say, each end is curved, but in opposite direc- 

 tions, and very often in planes at right angles to each other. When rods are 

 found in which the ends curve inward towards each other and in the same 

 plane, they are called C-shaped or "bracket "-shaped particles. Both sigmoid 

 and C-shaped rods may occur in the same individual. 



Key to the Genera of Chiridotin^. 



.1. — No sigmoid bodies; wlieels present, collected in little papillae (plate vii, fig. 24). 



Tentacles 12 (10-14) ; ciliated funnels mostly single and scattered (plate vii, figs. 



23, 28) Chiridota 



Tentacles 18 (16-20) ; ciliated funnels mostly single and scattered (plate vii, figs. 



14) Polycheira 



AA. — Sigmoid or bracket-shaped bodies or minute curved rods present (plate vii, figs. 3, 6, 9, 

 10, 11, 27). 



B. — Wheels present, in papillae T.4;niogyrus 



BB. — Wheels present, but scattered Trochodota 



BBB. — Wlieels wanting. 



Sigmoid bodies present Scoliodota 



Sigmoid bodies wanting; minute curved rods present Toxodora 



AAA. — Deposits wholly wanting Achiridota 



