MOKOGRAPH OF THE EXISTING CRINOIDS. 



155 



the longitudinal axis of the arm. Their component segments either are fitted 

 closelj^ end to end, or the more proximal, sometimes all, have their angles cut 

 away, admitting of motion in a plane parallel to the dorsoventral plane of the 

 arm: there is no provision for 

 lateral motion. The earlier geni- 

 tal pinnules stand up like the 

 oral pinnules, those of the two 

 sides of the arm being parallel 

 with each other, and the distal 

 ends are always more or less 

 curved outward toward tiie arm 

 tips. Going outward along the 

 arm the later genital pinnules 

 are seen gradually to bend lat- 

 erally outward, this being cor- 

 related with the gradual develop- 

 ment of a lenticular space be- 

 tween the first and second seg- 

 ments by which it is chiefly ox- 

 commodated. As the genital 

 pinnules begin to assume the 

 character of distal pinnules their 

 recumbenc}'' increases until the dis- 

 tal pinnules are reached. These 

 latter extend outward horizon- 

 tally at right angles to the dor- 

 soventral plane of the arm. 



Typically the distal pinnules 

 consist of about 20 segments, 

 though there may be as many as 

 30. They are almost always 

 longer than, usually from half 

 again to twice as long as, the 

 genital pinnules, and as a rule 

 equal the longest oral pinnules 

 in length. They are extremely 

 slender and delicate; the first 

 segment is trapezoidal, the long- 

 est side outward, or more or less 

 crescentic, about twice as broad 

 as long; the second is trapezoidal, the longest side inward (directed proximally). 

 about twice as long as the first, or about twice as long as the proximal width ; the 

 third segment is squarish, or somewhat longer than broad, and the next two or 

 three increase rapidly in length, the outer being from two to four times as long 

 as broad terminally, usually with more or less swollen and slightly overlapping 



13 — Lateiul view of ttpe specimen op Cosmiometea 



CliASSICIRBA. 



