A MONOGRAPH OF THE EXISTING CRINOIDS 141 



Syzygies occur between brachials 3+4, 9+10 (sometimes between brachials 

 10 + 11 or 11 + 12), from between brachials 13 + 14 to between brachials 15 + 16 

 (usually between brachials 14 + 15), and from between brachials 17 + 18 to between 

 brachials 19 + 20 (usually between brachials 18 + 19); on arms arising from a IIBr 

 or IIIBr axillary the second and sometimes also the third syzygy is omitted. The 

 distal intersyzygial interval is from 2 to 10 muscular articulations, varying in different 

 individuals, or sometimes on different arms, from 2 or 3 to 7-10 (usually 9 or 10); it 

 is most commonly 3 or 4 muscular articulations on arms arising from a IBr axillary, 

 and 7-10 muscular articulations on arms arising from a IIBr or IIIBr axillary. 



Pa is usually absent, but occasionally present on one, two, or a few arms, and in 

 rare cases may be present on as many as half the arms. Pj and Pb are longer and 

 stouter — often very much stouter — than the other pinnules, though P, and Pc some- 

 times approach them more or less closely in length and stoutness. The earlier seg- 

 ments of these pinnules may be smooth, or they may be slightly carinate on the 

 distal side. The longest segments of P2, Pb, P3, and Po are usually between two and 

 three times as long as broad, and, while they may be smooth, or almost smooth, they 

 are commonly more or less sharply prismatic with serrate or spiny distal ends that 

 rarely are produced into processes suggesting those on Pj in certain forms of Oligometra 

 serripinna. 



Pi is from 2 to 6 (usually from 3 to 4) mm. in length and consists of from 6 to 18 

 (usually 10-15) smooth segments most or all of which are somewhat longer than 

 broad, those in the distal half being usually about half again as long as broad. P, is 

 always absent on the inner of the two arms arising from a IIIBr axillary, and some- 

 times also on the inner arms borne on a IIBr axillary, but it is sometimes present on 

 the latter, and it is always present on the two outermost arms arising from each post- 

 radial series. When present on an inner arm from a IIBr axillary Pi is usually 

 smaller with fewer segments than its fellow on the outer arm from the same axillary. 

 Though usually slightly stiffened, Pi may be weak and flexible, or considerably 

 stiffened. 



P2 is longer and more or less, though sometimes not much, stouter than Pi ; it is 

 sometimes twice as long as P] and may be much stouter, but usually it is from about 

 one-quarter to one-half again as long as Pi and proportionately stouter. It is more or 

 less strongly stiffened, and may even be almost spinelike. It varies from 3.5 to 12 

 mm. in length, being usually from 4 to 6 mm. long, and is composed of 10-20 (most 

 commonly 13-17) segments of which the first is broader than long or about as long as 

 broad, the second is about as long as broad or slightly longer, the third is nearly or 

 quite twice as long as broad, and those following progressively increase in length, 

 reaching a length of from three to four or more times the width distally. The seg- 

 ments are often more or less strongly prismatic, and the distal ends are usually, 

 though not always, armed with more or less conspicuous spines, especially at the 

 prismatic angles. Pb resembles Pj and is similar to it though usually somewhat 

 smaller. It varies from 2.2 to 5.5 mm. in length, being usually between 3.5 and 5.5 

 mm. long, and is composed of 9-16 (usually 12-14) segments. P3 is usually more or 

 less smaller than P2, sometimes being not even half so large, even smaller than Pi; but 

 it is occasionally nearly or quite equal to Pj, and in rare cases may even be longer and 

 stouter. It is from 1.9 to 8 (most commonly from 2 to 4) mm. long, and is composed 



