296 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



Promachocrinus (Florometra) magellanica A. H. Clark, Die CrinoSden der Antarktis, 1915, p. 105 

 (collected by the Challenger, recorded as rhomboidea), p. 106 (collected by the Alert and Vettor 

 Piaam"), p. 142 (synonymy; summary of previous records; range), pi. 8, figs. 1-5. 



Dicujnostic features [bj' A.M.C.].— A species of Florometra with the basal segments 

 of the pinnules enlarged and carinate ; P, and Pj are similar in length and number of 

 segments and their relative proportions seem to be more constant than in most species 

 of the genus; the third syzygy is usually between brachials 16+17; the cu-ri are LX-C, 

 the longest with 40 to 65 segments and measuring up to 65 mm. in length when the 

 breadth at the first syzygy is 2.5 mm. ; the size can be large with the arms up to 200 mm. 

 in length. 



Description. — The centrodorsal is hemispherical, rather large, \vith a deep pit about 

 2 mm. in diameter at the dorsal pole; the sides up to this pit are entirely covered with 

 cirrus sockets, the distal slightly smaller than the peripheral, arranged in alternating 

 rows. 



The cirri are LX-LXX, 30-50 (usually 40-50), resembling those of the other species 

 of the genus; the longest cirrus segments are about three times as long as broad in the 

 longest cirri, about twice as long as broad in the shorter. 



The distal edges of the radials are even with the margin of the centrodorsal and 

 are only visible as very low triangles in the interradial angles. The IBri are very short, 

 mth the lateral edges not quite in contact basally and strongly convergent, making an 

 angle with each other of nearly 90°, and the distal border more or less strongly depressed 

 by a rounded posterior projection from the axiUaries which may meet the centrodorsal, 

 excluding the IBri from view in the median line. The lateral borders are somewhat 

 concave. The ventrolateral edges are extended laterally in a triangular flangelike 

 process the proximal apex of which lies beneath the proxunal lateral angles. The IBr2 

 (axillaries) arc ahuost triangular, about as long as broad, with the distal angle produced, 

 truncated, and notched, the anterior sides nearly straight, slightly everted and finely 

 spinous, and the pro.ximal border with a broadly rounded process incising the IBrj. 



The 10 arms are about 190 mm. long. The first brachials are about four times as 

 long exteriorly as interiorly, very obliquely wedge-shaped, with the distal border slightly 

 depressed in the middle by a process from the second brachial, and the short inner sides, 

 which are not in contact basally, making a very broad angle, almost a straight line, with 

 each other; the outer side is somewhat produced, the production being markedly flat- 

 tened and studded with very fine spines. The second brachials are somewhat larger than 

 the first, irregularly quadrate, with the somewhat promment distal edge and the portion 

 beneath the pinnule socket fuiely spinous. The first syzygial pair (composed of brach- 

 ials 3+4) is from half again to about twice as long interiorly as exteriorly, wedge- 

 shaped, with the distal border rather prominent and, like the syzygial Ibe, finely serrate. 

 The following 7 or 8 brachials are slightly wedge-shaped, about twice as broad as the 

 median length, with prominent and finely serrate distal ends, after which the brachials 

 become almost or quite triangular, about as long as broad, \vith serrate ends which in- 

 crease in prominence as the brachials become wedge-shaped again distally. 



Syzygies occur between brachials 3+4, 9+10, 16+17, and distally at intervals of 3 

 muscular articulations. 



Pi is from 20 to 22 mm. long, slender and flagellate, tapering rather rapidly on the 

 first 6 segments, much more gradually from that point onward, composed of 50 segments, 

 of which the first is rather large, about twice as broad as long, the second is much shorter, 



