A MONOGRAPH OF THE EXISTING CRINOIDS 93 



Crotalometra marginalia A. H. CLARK, Unstalked crinoids of the Si&oja-Exped., 1918, p. 149 (in key; 



range), p. 150 (detailed description; station 226), p. 274 (listed), pi. 23, fig. 62. Gisi/fiN, Ark. 



Zool., vol. 19, No. 32, Feb. 20, 1928, p. 8 (probably a large specimen of C. magnicirra). 

 Crotalomelra eridanella A. H. CLARK, Journ. Linn. Soc. (Zool.), vol. 36, No. 249, April 1929, p. 635 



(listed), p. 654 (off Great Nicobar, 1,040-1,120 fathoms; description), pi. 42, fig. 9. 

 Crotalometra marginata GIBL^N, Kungl. Fysiogr. Sallsk. Handl., new ser., vol. 45, No. 11, 1934, p. 23. 



Diagnostic features. The brachials of the middle and outer portions of the arms 

 have the central portion of the distal edge somewhat produced and spinous. The 

 13-20 arms are 90-150 mm. long, and the cirri are 55-85 mm. long with 45-70 segments. 



Description. The centrodorsal is apparently as in C. magnicirra, with the cirrus 

 sockets arranged in 10 columns, two in each radial area. 



The cirri are XX, about 70 (69 to broken tip), 85 mm. long, large and stout. The 

 first three segments are subequal, about three times as broad as long, the fourth is 

 slightly longer, the fifth is about as long as broad or slightly longer than broad, and those 

 following are about one-third again as long as broad, becoming as long as broad after 

 the eighteenth and after four or five more about twice as broad as long. The eighteenth 

 is a transition segment. Following the transition segment the dorsal surface of each 

 segment gradually rises into a subterminal dorsal tubercle which, however, never 

 projects in the form of a spine. The tubercle is at first rather broad transversely and 

 rounded dorsally, but distally it becomes narrower so that the dorsal surface of the 

 segment becomes bluntly carinate. Viewed laterally the dorsal profile of the cirri 

 presents a slightly serrate appearance. 



The ends of the basal rays are visible as prominent dorsoventrally elongated 

 tubercles in the iuterradial angles of the calyx. 



The radials project very slightly beyond the rim of the centrodorsal. The IBri 

 are very short and bandlike, about five times as broad as long, with the proximal 

 border convex and the distal concave, and are in close lateral apposition. The IBr 2 

 (axillaries) are broadly pentagonal, half again as broad as long, with all the sides 

 strongly concave. The lateral borders of the two components of the IBr series taken 

 together are evenly and strongly concave, the proximal width of the IBri and the distal 

 width of the IBr 2 being about the same. Both these ossicles are sharply flattened 

 laterally with the apposed edges somewhat everted. The IIBr series are 4(3 + 4), very 

 strongly rounded dorsally like the IBr series, in close lateral apposition and sharply 

 flattened against their neighbors. The lateral edges are somewhat produced. The 

 elements of this division series are relatively rather long. 



The 20 arms are about 150 mm. long, deep and laterally compressed, and strongly 

 rounded dorsally. The first brachials are very short and strongly concave distally. 

 The second brachials are much larger with a posterior process incising the first. The 

 first syzygial pair (composed of brachials 3 + 4) is about as long as broad with the dorsal 

 and lateral profiles concave as in the syzygial pair formed by the two distal elements of 

 the I IBr series. The following brachials to the ninth are wedge-shaped, half again as 

 broad as long. The brachials following are triangular, about as long as broad, in the 

 terminal portion of the arm becoming wedge-shaped again and slight!} 7 longer. After 

 the proximal third of the arm the brachials develop prominent and spinous distal ends 

 and a striated dorsal surface. 



Syzygies occur between brachials 3 + 4, again from between brachials 15 + 16 to 

 between brachials 19 + 20, and distally at intervals of from 4 to 9 muscular articulations. 



