A MONOGRAPH OF THE EXISTING CRINOIDS 237 



GLYPTOMETRA CRASS A (A. H. Clark) 



PLATE 21, FIGURE 68 



Pachylometra crassa A. H. CLARK, Proc. Biol. Soc. Washington, vol. 25, 1912, p. 77 (description; 

 Siboga station 259). 



Perissomelra crassa A. H. CLARK, Journ. Washington Acad. Sci., vol. 6, No. 17, 1916, p. 607 (listed); 

 Unstalked crinoids of the Siboga-Exped., 1918, p. 177 (in key; range), p. 181 (detailed descrip- 

 tion; station 259), p. 275 (listed), pi. 24, fig. 66. GISLEN, Vid. Medd. Dansk Naturh. Foren. 

 K0benhavn, vol. 83, 1927, p. 35. A. H. CLARK, Journ. Linn. Soc. (Zool.), vol. 36, No. 249, 

 April 1929, p. 658 (compared with P. occidentalis) . GISLEN, Kungl. Fysiogr. Sallsk. Handl., 

 new ser., vol. 45, No. 11, 1934, p. 22. 



Perissometra gorgonia A. H. CLARK, Journ. Washington Acad. Sci., vol. 6, No. 17, 1916, p. 607 (listed; 

 nomen nudum); Unstalked crinoids of the St'6offa-Exped., 1918, p. 177 (in key; range), p. 179 

 (detailed description; stations 254, 294), pp. 274, 275 (listed); Journ. Linn. Soc. (Zool.), vol. 36, 

 No. 249, April 1929, p. 658 (south of the Nicobar Islands; 560 fathoms; notes). GISLEN, Kungl. 

 Fysiogr. Sallsk. Handl., new ser., vol. 45, No. 11, 1934, p. 22. 



Diagnostic features.- The longest earlier cirrus segments are nearly as long as 

 broad, the distal being somewhat shorter and usually with a small well-rounded sub- 

 terminal dorsal tubercle; the lower brachials have the distal edges prominently everted 

 or thickened, usually forming conspicuous half rings across the dorsal surface of the 

 arms; the 10-20 arms are 100-180 mm. long; and the cirri are 25-32 mm. long with 

 usually about 20 segments. 



Description of the type specimen. The centrodorsal is very large, 5 mm. across the 

 irregularly convex dorsal pole and 5 mm. high; it is truncated conical, the sides making 

 a rather small angle with each other. The cirrus sockets are arranged in 10 columns, 

 usually 3 to a column; the columns are closely crowded interradially and slightly 

 separated in the midradial line 



The cirri are about XXV, 18-22 (usually 20), from 25 to 32 mm. long, stout and 

 short-segmented. The first segment is short, those following gradually increasing in 

 length so that the sixth and following are nearly as long as broad, those in the distal 

 third of the cirri being slightly shorter again. On the seventh a slight broad subterminal 

 dorsal hump makes its appearance which slowly increases in height so that the terminal 

 nine possess a prominent broad, blunt, and well-rounded subterminal tubercle which 

 becomes more pointed on the last two or three before the penultimate. The opposing 

 spine is small, subterminal, resembling the tubercle on the preceding segment, but 

 arising from a much smaller base. 



The ends of the basal rays are concealed. 



The radials are concealed. The IBri are very short, broadly V-shaped, sometimes 

 concealed in the median line so that only the lateral portions are visible ; the dorsal sur- 

 face is more or less irregular. The IBr 2 (axillaries) are short and broad, nearly three 

 times as broad as long, rhombic with the lateral angles truncated so that the lateral 

 edges are nearly or quite as long as those of the IBr,. The IIBr series are 4(3+4). 



The 10-11 arms are about 180 mm. long. The first two brachials are about equal 

 in size, slightly wedge-shaped (more pronouncedly so on the second), about three times 

 as broad as the median length. The broad and smooth synarthrial tubercles are 

 scarcely marked. The brachials have slightly produced distal edges and a more or less 

 swollen dorsal surface. 



