A MONOGRAPH OF THE EXISTING CRINOIDS 655 



P D and the pinnule on the IIIBr series (when present) are long, the latter being 

 shorter than the former. P[ is still shorter, and the length of the succeeding pinnules 

 gradually diminishes to those of the fifth and sixth brachials, which are the shortest 

 on the whole arm. From the seventh brachial onward the pinnules arc long and stout, 

 gradually increasing in length and thickness to near the middle of the arm. The 

 thickness is greatest in the short posterior arms, in which both length and tliickncss 

 rapidly decrease from the middle to the end of the arm, while in the long anterior 

 arms the thickness slowly diminishes and the length slightly increases, so that the 

 terminal pinnules are long and slender. The last 6 or 8 segments of the pinnules of 

 the division series and of the first 9 or 12 brachials have the outer ventral margin of 

 each ossicle produced into a small lancet-shaped process which bends over toward the 

 ventral side, so that the end of the pinnule has a comblike appearance. Many of the 

 other pinnules until near the end of the arm have similar processes on their 4 or 5 

 terminal segments. 



The disk is about 20 mm. in diameter. Small calcareous concretions are occa- 

 sionally present in the neighborhood of the peristome and of the anal tube. The 

 mouth is excentric and interradial. The posterior ambulacral grooves are very in- 

 distinct, and often nearly obliterated. 



The color in alcohol is from yellowish brown to dark brown. 



Carpenter said that the width of the basal cirrus segments somewhat exceeds the 

 length, but in the second and third segments this disproportion between the length 

 and breadth is reduced, and in the fourth it becomes reversed, the length of the fourth 

 segment being slightly greater than its width. In the fifth and sixth segments the 

 length is half again as great as the width, and a very slight degree of lateral compres- 

 sion is visible in the sixth segment, while the fifth, like the 4 preceding, is cylindrical, 

 or nearly so. The fifth and sixth are the 2 longest segments of the cirrus, and from 

 this point onward the length of the segments gradually decreases, until in the tenth 

 and following segments it becomes again less than the width. At the same time the 

 transverse diameter, which in the first 5 cylindrical segments is equal to the dor- 

 soventral width, undergoes in the seventh and eighth a sudden decrease. A faint 

 indication of this is seen in the sLxth segment, and it is continued on to the end of the 

 cirrus, so that its terminal portion exhibits a considerable degree of lateral compres- 

 sion. In correspondence with this, a small spine gradually develops on the distal 

 dorsal margin of the sixth and following segments, on which it becomes progressively 

 more and more marked, until on the penultimate segment it becomes a short pointed 

 opposing spine. This series of small spines seems to be characteristic of those cirri 

 only which have reached their full development, for scarcely any trace of them is 

 visible in the still immature cirri. 



The details of the 8 specimens considered by Carpenter as typical polymorpha 

 are as follows: 



There are 13 arms, the 3 IIBr series being 4 (3 + 4). 



There are 18 arms, 4 of the IIBr series being 4 (3 + 4) and 4 being 2. 



There are 20 arms; of the IIBr series, 5 are 4 (3 + 4) and 5 are 2. On one of the 

 arms the earlier syzygies occur between brachials 5 + 6, 14+15, and 18+19. 



There are 25 arms; all 10 of the IIBr series are 4 (3 + 4); of the IIIBr series, 3 

 are 2 and 2 are 4 (3 + 4). 



