102 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



vol. 61, No. 15, 1913, p. 46 (published references to specimens in the B. M.; Challenger Sta. 344; 

 characters of the cirri); Unstalked crinoids of the Siboga-Exped., 1918, p. 148 (in key; range), 

 p. 149 (references); The Danish Ingolf-Exped., vol. 4, No. 5, Crinoidea, 1923, p. 40 (range); 

 Gislen, Zool. Bidrag Uppsala, vol. 9, 1924, p. 28, footnote. — Mortensen, Handbook of the 

 echinoderms of the British Isles, 1927, p. 25 (localities; in key). — Gislen, Ark. Zool., vol. 19, 

 No. 32, Feb. 20, 1928, p. 7, No. 30 (notes); Kungl. Fysiograf. Sallsk. Handl., new ser., vol. 45, 

 No. 11, 1934, p. 23. 



Thulassometra multispina (part) A. H. Clark, Smithsonian Misc. Coll., vol. 61, No. 15, 1913, p. 47 

 (the pentacrinoid from Challenger station 344). 



Crotalometra porrceta Gislen, Zool. Bidrag Uppsala, vol. 9, 1924, p. 194 (supposed larva). 



Diagnostic features. — The cirri have 40-50 segments and are 55 mm. long; the 20 + 

 arms are 150 mm. long. 



Description. — The centrodorsal is a thick disk with the interradial angles slightly 

 produced. 



The cirri are XX-XXX, 40-50, long and stout (according to the figure about 55 

 mm. long). The longest proximal segments are about as long as broad, but most of the 

 segments are broader than long and are produced on the dorsal side into a strong 

 pointed process which at first involves only the distal portion but later rises from most 

 of the dorsal surface. 



The radials are invisible except in the interradial angles of the calyx. The elements 

 of the IBr series are rather convex and are slightly tubercular at the articulation 

 between them. The IBrj are short, laterally united, and the IBr 2 (axillaries) are 

 broadly pentagonal, about two and one-half times as long as the IBri. The IIBr 

 series are 4(3+4) and the IIIBr series, when present, are 3(2 + 3). The elements of 

 the division series are very convex and have their sides flattened against each other, 

 but this is less marked on the outside of the postradial series where the hypozygals of 

 the IIBr and IIIBr axillaries and the second brachials are kept apart by the large 

 pinnule on the segment preceding. 



There are 20+ arms, probably 150 mm. long. They are composed of compressed 

 triangular brachials which become elongated and quadrate distally. From the four- 

 teenth brachial onward the middle of the distal edge of each ossicle is raised into a 

 strong plate the front face of which is hollowed. Beyond the eleventh or sixteenth 

 brachial this gives place to an overlap of the usual character that extends far out on 

 the arm. 



Syzygies occur between brachials 2 + 3, again from between brachials 7 + 8 to 

 between brachials 15+16, and distally at intervals of from 4 to 13 muscular articula- 

 tions, the intervals becoming shorter toward the end of the arms. 



Pi and the preceding pinnules on the IIBr 2 and IIIBri are tolerably equal with 

 about 15 stout segments the five lowest of which are rather broad and trihedral with 

 lluttcned outer faces and the inner sides slightly beveled away. P» and P s are smaller 

 with fewer segments of which the basal arc more compressed. The pinnules following 

 are Larger again with broader lower segments the outer edge of which is expanded 

 toward the ventral side. This feature gradually dies away in the outer parts of the 

 arms, and the segments become more elongated. 



Tin' disk is 15 nun. in diameter, slightly incised and well plated like the brachial 

 ambulacra. The pinnule ambulacra have well defined side plates and small sacculi. 



The color in alcohol is dark gray-brown. 



