294 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



by a muscular articulation; in cither case there may be a syzygy between brachials 3+4, 

 more rarely between brachials 5+6. On one arm there are syzygies between both 

 brachials 3+4 and 5 + 6. The next syzygy, whether a second syzygy is present or not, 

 lies fairly constantly from about between brachials 13 + 14 to between brachials 20+21, 

 most commonly between brachials 15+ 16 or 16 + 17. The following intersyzygial inter- 

 val is from 4 to 14 muscular articulations, in most cases from 6 to 10. 



Because of the regular presence of IIBr series the number of arms is as a rule 20, 

 but as the arms are often broken Hartlaub could not determine this with certainty. 

 Only the specimen from St. Vincent possesses more than 20 arms, and the largest from 

 Blake station 157 has only 18. The proximal brachials are rectangular and broader 

 than long; at about the fifth to the tenth the brachials become bluntly wedge-shaped, 

 and at about the middle of the arm their dorsal surface is approximately triangular. 

 The arms taper slowly distally. 



The lowest pinnule on arms following the IBr axillary or a IIBr 2 series is Pi, on 

 postradial series with the IIBr 4(3+4) it is P D . P D is about 8 mm. long with 30 seg- 

 ments of which about the first ten are unusually thick, broad, and carinate, and on the 

 interradial side smooth in correlation with the sharply flattened sides of the IIBr 

 series. The segments following are more slender and small. Here and there spines 

 or teeth are found on the edges of the segments. P D is dark colored as far as the dark 

 color extends on the postradial series. On the two arms arising from a IBr axillary 

 studied Pi is somewhat longer than P D and is composed of 34 segments of which the 

 first ten are broad and flat; the pinnule tapers gradually; the fourth-seventh segments 

 have a strikingly strong single keel. On arms arising from a IIBr axillary P! differs from 

 the pinnule described. It is very variable in the form of the basal segments, not only 

 in different specimens, but strikingly so on different arms of the same specimen. For 

 instance, on the same postradial series one outer Pi is 7 mm. long and has six broad 

 proximal segments which in surface view appear heartshaped or approximately triangu- 

 lar with proximally directed points; a carination is scarcely suggested. The other outer 

 Pi is 6 mm. long with 10 much broader proximal segments of which the form is more 

 quadrangular; its most striking feature is a typical double keel; the crests of the keels 

 as far as the fifth segment on one side, thence on both sides, are beset with spines and 

 teeth, or serrate. The small distal segments of the two pinnules are also different. 

 Neither pinnule follows a P D so that their positions are entirely comparable. Only 

 in the majority of cases can the following be said of Pi. It is composed usually of 20-25 

 segments of which the 8-10 proximal, with the exception of the first, are doubly keeled, 

 the crest of the carination being spiny or serrate on one or on both sides. The proximal 

 segments are more closely united than in P D , in which they follow each other rather 

 closely. The small distal segments arc sometimes more triangular, sometimes more 

 rectangular. Proximally rather broad, Pi tapers only gradually to a fine point. P, 

 and P» are in general shorter than Pi, usually 5-7 mm. long with 16-23 segments of 

 which the edges arc in part dentate or spiny. But there is marked variation in the 

 length and in the number of included segments. The number of segments may vary 

 as much as 10 in the same specimen, as for instance in the largest specimen from Blake 

 station 157 in which P a has from 17 to 27 segments. In the same specimen one Pj is 

 over 10 mm. long with about 35 segments and of the same length as Pi on the same arm. 

 In the specimen from Blake station 158 one P, is barely 3 mm. long with 10 segments. 



