A MONOGRAPH OF THE EXISTING CRINOIDS 219 



Pachylometra in 1909 robusta was transferred to it, and laterjn the_same year I com- 

 pared Pachylometra robusta with the new species P. macilenta. In my jnemoir on the 

 crinoids of the Indian Ocean published in 1912 Pachylometra robusta\.*as listed and the 

 synonymy and original locality were given. In my notes on the crinoids of the British 

 Museum published in 1913 I recorded a specimen from the Sahul Bank that had been 

 included under Antedon pa-tufa by Prof. F. Jeffrey Bell in his'account of the crinoids of 

 that area. On the creation of the genus Perissornetra in 1916 I transferred robusta to it. 

 After an examination of Carpenter's type specimen in the British Museum Prof. 

 Torsten Gislen gave notes on it and remarked that this species, considered by me to be a 

 Perissmnetra, should be referred to Monachometra. 



MONACHOMETRA FRAGILJS (A. H. Clark) 



PLATE 20, FIGURES 62, 63 

 [See also vol. 1, pt. 2, figs. 824-830, p. 399.] 



Pachylometra fragilis A. H. CLARK, Proc. Biol. Soc. Washington, vol. 25, 1912, p. 79 (description; 



Siboga station 166). 

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



Unstalked crinoids of the Siboga-Exped., 1918, p. 185 (detailed description; station 166; also 



Albatross station 5110), p. 273 (listed), pi. 24, figs. 68, 69. [GISLEN, Vid. Medd. Dansk. Nat. Foren. 



Kpbenhavn, vol. 83, 1927, p. 38 (comparisons) ; Kungl. Fysiogr. Sallsk. Handl., new ser., vol. 



45, No. 11, 1934, pp. 18, 21.] 

 [Monachometra cf. fragilis GISLEN, Zool. Bidrag Uppsala, vol. 9, 1924, pp. 44, 51, fig. 14, p. 48 (base 



of a post-radial series).] 



Diagnostic features. The brachials in the proximal portion of the arms have un- 

 modified distal edges; the centrodorsal is low, flattened hemispherical, with the cirrus 

 sockets arranged in 15 closely crowded and somewhat irregular columns; the 19 arms 

 are 145 mm. long; and the cirri have 17-20 segments. The synarthries are unusually 

 brittle. 



Description. The centrodorsal is low, flattened hemispherical, 7 mm. in diameter 

 at the base and 3 mm. high; in general the centrodorsal resembles that of the species of 

 Crinometra. The cirri are closely crowded and are arranged approximately in 2 or 3 

 irregular rows and 15 columns, 3 in each radial area; the sockets in the proximal row 

 reach the rim of the centrodorsal. 



The cirri are about XXX, 17-18, from 30 to 35 mm. long and are moderately 

 slender. The first four segments are short, the fifth is half again as long as broad, the 

 sixth to eighth are twice as long as broad, and those following gradually decrease in 

 length so that the distal are about as long as broad, the terminal increasing again so 

 that the antepenultimate and penultimate are about twice as long as broad. The longer 

 proximal segments have slightly prominent ends, while the shorter distal have the dorsal 

 distal margin slightly swollen. 



The ends of the basal rays are large and prominent, forming rhombic areas in the 

 angles of the calyx. Deep, though very narrow, subradial clefts arc present. 



The radials are very short, strongly curved, with a low, broad, and obscure median 

 tubercle. The IBr ( are exteriorly very short, bandlike, with an obscure low median 

 tubercle. The articular face is produced toward the center of the calyx so that their 

 sharply flattened lateral borders almost meet, being separated only by a narrowly 



