566 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The five radials, almost as high as broad and hexagonal in shape, are already 

 so large that they are almost in contact with each other at the lower extremity 

 of their lateral borders, which are separated from those of their neighbors by a 

 narrow vertical fissure. 



On the distal straight border of each of the radials there has appeared a 

 IBr 15 which is elongated and as high as, though scarcely half as broad as, the radial. 



The orals are in the same condition as in the preceding stage. 



In one of the interradial spaces, at the level of two of the radials and between 

 them, a small plate, oval in shape, with the longer axis parallel with the stem, 

 which with its proximal border touches the distal angle of a basal and distally 

 overlaps the proximal border of an oral, has appeared. This is the radianal. 



Three specimens, taken at the same place, time, and depth as the two preced- 

 ing, are at a more advanced stage. One of these was attached to the tube of a 

 Pectinaria hyperborea, and the two others to the stalk of a Cellularia ternata var. 

 gracilis. 



The length of these specimens is 10 mm. 



In one of them the column is composed of 27, in the other of 29 segments. 

 The five proximal columnals are strongly compressed along the axis of the stem, 

 the others being as in the preceding stages. 



The crown, which is 0.75 mm. long, shows many changes. 



The radials are all united by their lateral borders. On the distal border of 

 the IBr 15 which is still very narrow, there has developed a IBr 2 (axillary) which 

 is of about the same height and width as the IBr 15 and beyond it the two arms 

 are in course of development. 



The elements of the IBr series are very narrow and are very widely separated 

 from their neighbors. 



The arms are 0.75 mm. long, directed upward, or sometimes more divergent, 

 with the ends pointed and slightly bent inward, and are composed of as yet only 

 six segments which are longer than broad, and already comparable to those of 

 the adult in which, however, they are broader than long, especially in the proximal 

 portion of the arms. 



The dorsal portion of the brachials, of which the distal border overlaps slightly 

 the proximal border of the brachial succeeding and is armed with minute conical 

 points, is deep, semicylindrical, and composed of a calcareous network crowded 

 with little rounded meshes. The two lateral portions are very thin and mem- 

 branous, and the distal part of their border turned inward, or ventrally, forms 

 a rounded flap. In the fully grown pentacrinoid and in the adult the ventral 

 border of each brachial has two or three similar flaps. 



Each of these flaps is supported by a long and slender calcareous rod or 

 spicule situated within it, usually somewhat S shaped, which is directed obliquely 

 upward and inward, and of which the end, situated near the ventral border of 

 the segment, is a little enlarged and pierced with a larger or smaller number of 

 small round holes. The opposite end, situated near the dorsal calcareous network, 

 is pointed, or sometimes bifurcated. 



