PART 6 A MONOGRAPH OF THE EXISTING CRINOIDS 775 



are by no means the same but in a quite constant ratio of 1 :1.6, the second being dis- 

 tinctly longer on all the arms. Since the type has the centrodorsal 9 mm. in diameter, 

 like the types of both rugosus and borealis, there is no distinction of size between the 

 three species and only the different numbers of cirrus sockets and the more conical 

 shape of the centrodorsal in borealis (though this appears to be but 0.5 mm. higher 

 than that of naresi) seem to distinguish them, unless the different development of 

 the articular tubercles is found to be constant in the Hawaiian rugosus as opposed to the 

 other two species. 



The Siboga specimen of naresi has the Br 2 no longer than the B^ according to 

 Mr. Clark, but in view of the intermediate proportions of the type compared with 

 borealis I do not think this is significant. 



THAUMATOCRINCS BOREALIS (A. H. Clark) 



Decametrocrinus borealis A. H. CLARK, Proc. U.S. Nat. Mus., vol. 33, 1907, p. 71 (description; Albatross 

 sta. 4918); vol. 34, 1908, p. 216 (compared with D. rugosus}, p. 319 (Japan); Crinoids of the 

 Indian Ocean, 1912, p. 248 (considered as a synonym of D. naresi); Smithsonian Misc. Coll., 

 vol. 61, No. 15, 1913, p. 66 (a valid species; comparison with naresi). 



Thaumatocrinus borealis A. H. CLARK, Smithsonian Misc. Coll., vol. 61, No. 15, 1913, p. 67 (com- 

 parison with T. naresi); Journ. Washington Acad. Sci., vol. 5, No. 6, 1915, p. 215 (southern 

 Japanese type; range and its significance); Die Crinoiden der Antarktis, 1915, p. 149 (in key), 

 p. 150 (range); Unstalked crinoids of the Siboga-Exped., 1918, p. 259 (in key; range), p. 260 

 (specific validity). 



Diagnostic features. The size of the unique type specimen is rather large, the 

 arms being about 125 mm. in length and the centrodorsal 9 mm. broad at the base. 

 The second brachial is twice as long as the first, which is disproportionately small 

 and is excavated by a rounded proximal production of the lower border of the second, 

 and the centrodorsal is low conical bearing about LXXX cirri, there being at the 

 periphery 6 to 8 sockets beneath each radial. 



Description. The centrodorsal is low conical with the sides swollen, 9 mm. broad 

 at the base and 4 mm. high. There is a moderately large bare polar area. The cirrus 

 sockets are closely crowded, arranged in from 2 to 4 rows, with from 6 to 8 beneath 

 each radial about the periphery of the centrodorsal. 



The cirri, about LXXX, are all lacking. 



The ends of the basal rays, flush with the surface of the centrodorsal, are just 

 visible in alternate interradial angles. 



The 10 arms are about 125 mm. long. The first brachials are short and oblong, 

 about 3 times as broad as long, entirely separated from their neighbors. The second 

 brachials are much larger, not quite twice as broad as long, with the proximal edge 

 somewhat produced posteriorly and with the distal edge of the first forming a slight 

 tubercle. The following brachials to about the fifteenth are wedge-shaped, about twice 

 as broad as their median length, those succeeding becoming gradually more obliquely 

 wedge-shaped and then triangular, about as long as broad, distally wedge-shaped again 

 and finally elongate. 



Syzygies occur between brachials 4+5, 9 + 10 or 10 + 11, and distally at intervals 

 of from 3 to 7 (usually 4 or 5) muscular articulations. 



PI, on the second brachial, is 15 mm. in length, long, slender, evenly tapering and 

 gradually becoming flagellate distally, composed of 45 to 50 segments, of which the basal 

 5 or 6 are broader than long with the corners cut away, those following are about as 



