THE APODOUS HOLOTHUKIANS 173 



orly and usually with a distinct caudal portion, which is generally one-third of 

 the total length or even more. Radial pieces of calcareous ring with conspicu- 

 ous, bifurcate, jjosterior prolongations. Calcareous deposits of very various 

 kinds, with no particular kind characteristic of the genus. Phosphatic deposits 

 are usually entirely wanting and are known to occur in only one species. 



The holothurians composing this genus may usually be recognized by the 

 form of the body, but there is no doubt that the differences between Caudina 

 and Molpadia are very slight and of little significance. The geographical dis- 

 tribution of the genus is interesting; three species are confined to the eastern 

 coast of the United States, two occur on the North American Pacific coast, and 

 the three others occur on the coast of Chile, one of these ranging to New Zea- 

 land, Australia, the East Indies, and Japan. Little is known of their habits, 

 save that they live buried in sand or mud with the tip of the caudal region ex- 

 posed ; they burrow by means of the tentacles, aided by movements of the body, 

 and feed on the organic matter in the sand or mud, which they take into the 

 mouth. Besides the following eight species, "Trochostoma albicans glabra" 

 (Theel, 1886a, p. 46), which appears to be closely related to C. albicans, should 

 probably be recognized as a ninth species. 



Key to the Species of Caudina. 



A. — No colored phosphatic deposits in skin. 



B. — Calcareous deposits in the form of tables with perforated discs and conspicuous 

 spires (plate x, figs. 11, 13). 



Discs of tables 90-140^1 in diameter; spire rather low and irregular, usually 



of 4 somewhat converging rods arenata 



Discs of tables 150-270^ in diameter; spire rather high and pointed, of 3 con- 

 verging rods ALBICANS 



BB. — Calcareous deposits not tables. 



C. — Calcareous deposits more or less well formed, shallow cups perforated by 4 



holes and closed by a cross, the bars of which are just over the holes, the 



relative proportions of solid parts and holes varying very greatly (plate ix, 



figs. 4, 5, 11, 13, 13). 



D. — Nearly all the cups complete and symmetrical, with rounded knobs on 



margin (fig. 4). 



Caudal appendage very distinct chilensis 



Caudal appendage not apparent, the body simply tapering to a blunt 



point OBESACAUDA 



DD. — Nearly all the cups incomplete and more or less asymmetrical, without 



knobs (figs. 11-13) contractacauda 



CC. — Calcareous deposits more or less flat, perforated plates of no particular form. 

 Plates with sharp projections on the surface (plate x. fig. 13)..californica 



Plates almost perfectly smooth (plate ix, fig. 8) planapertuea 



A A. — Colored phosphatic deposits present in skin pigmentosa 



