568 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The column, composed of 49 segments, forms in its distal half a pronounced 

 S-shaped curve. It is attached not only, as in most cases, by the terminal stem 

 plate but also at two higher places, to a foreign body, a Rhahdammina ahyssicola. 



In another specimen at the same develo]:)mental stage there arise from the 

 terminal stem plate some digitiform prolongations, of which two are bifurcated 

 one or more times. 



In a third, belonging to the following stage, the discoidal enlargement repre- 

 senting the terminal stem plate is of irregular form and incloses some sponge 

 spicules; a few other segments in the distal portion of the cohimn may also give 

 rise to tubercular or digitiform processes by which they are attached to foreign 

 objects. 



The three proximal columnals have become much more flattened than pre- 

 viously, almost discoidal — a feature still more accentuated in the next stage. 



In one of the interradial areas of the soft ventral disk, which has considerably 

 increased in .size, the anal tube has appeared. It already rises high above the 

 surface of the disk and is cjdindrical, slightly oval, or pyriform in shape. At 

 its summit a small round dark spot indicates the position of the anus. As in 

 the free stage the anal tube is approximately midway between the mouth and the 

 periphery of the disk, and consequently far from the place first occupied by the 

 primitive radianal. 



Just below the base of the anal tube there are found in the skin of the disk 

 two small rounded calcareous plates of which the lower covers with its di.stal border 

 the proximal border of the upper. The two occur almost in a vertical line, as if 

 they had been drawn out by the anal tube in the course of its development. These 

 calcareous scales seem to be the remains of the original radianal, which as an 

 entity has disappeared. 



From the groove between the calyx and the topmost columnal cirri have begim 

 to protrude, and, with them, the centrodorsal, to which they are attached, appears. 

 This plate, still very narrow or annular, increases very rapidly at the next stage, 

 forming a basin which very soon conceals the basals. 



The first cirri are five in number and radially situated. They are directed 

 upward, lying closely upon the interbasal sutures, and are cylindrical, almost 

 straight or slightly curved (following the contour of the surface of the basals), 

 still smooth and unarticulated, with the tip rounded and devoid of a hook or claw. 

 All are about of the same size, and their tips scarcely extend beyond the distal 

 border of the basals. 



The radials have not been appreciably altered. 



The arms have elongated a little, and are composed of from 18 to 20 brachials. 

 There is only a single pair of pinnules, which are longer than in the previous stage, 

 straight, and pointed at the tips. 



In another specimen, not more advanced in other respects, the five primitive 

 cirri have become four or five times as long as in the individual just described, and 

 are composed of seven or eight well-developed segments, of which the terminal is 

 already provided with two claws. 



