A MONOGRAPH OF THE EXISTING CRINOIDS 275 



GLYPTOMETRA INVENUSTA (A. H. Clark) 



PLATE 29, FIGURE 89 



Pachylometra invenusta A. H. CLARK, Proc. Biol. Soc. Washington, vol. 22, 1909, p. 149 (description; 

 1146'30" N., 9316'00" E. ; 569 fathoms) ; Crinoids of the Indian Ocean, 1912, p. 220 (syn- 

 onymy; detailed description; locality), fig. 40, p. 221. 



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

 Unstalked crinoids of the Si&oga-Exped., 1918, p. 178 (in key; range), p. 181 (references). 

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



Diagnostic features. The cirri, which are arranged in 15 columns on the centro- 

 dorsal, are 30-34 nun. long with 20-21 segments, of which the distal are markedly 

 longer than broad; the 12 arms are 170 mm. long; and the division series and lower 

 brachials have a rather fine rugose ornamentation, the proximal brachials each bearing 

 a median small rounded tubercle. 



Description. The original description of this species is quite unsatisfactory. I 

 said that this species is in general similar to Glyptometra macilenta, but differs in many 

 details. The centrodorsal is not described. In the figure it is shown as a broadly 

 truncated cone. The cirrus sockets in the radial area shown are 5 in number; there are 

 3 along the proximal border and 2 below, situated under the spaces between those above. 

 This presumably indicates a species with the cirri in 15 columns, though the centrally 

 situated cirrus socket may be adventitious. 



The cirri are XXIII, 20-21, from 30 to 34 mm. long, rather slender, resembling 

 those of Glyptometra macilenta. The proportions of the component segments are the 

 same as in that species, but the distal edges of the segments are slightly more thick- 

 ened, giving the cirri as a whole a somewhat rougher appearance. 



The IIBr series are 4(3 + 4). The elements of the IBr and IIBr series and the first 

 two brachials exteriorly and first three ulteriorly are in close lateral apposition and 

 sharply flattened laterally, with the apposed edges somewhat everted. The ornamen- 

 tation of the ossicles of the IBr and IIBr series is essentially as in G. macilenta. 



The 12 arms are 170 mm. long, slender, as in G. macilenta. The brachials have the 

 same proportions as those of G. macilenta, but the proximal subquadrangular brachials 

 have the distal ends thickened and everted, and the remaining brachials have rather 

 prominently overlapping distal edges. In the figure the proximal discoidal brachials 

 are shown each with a small central tubercle. 



The distal intersyzygial interval is 4 or 5 oblique muscular articulations. 



The pinnules resemble those of G. macilenta, but the genital pinnules are more 

 swollen than are those of that species. 



The color in alcohol is dull yellowish white. 



Locality. OS South Andaman Island (lat. 1146'30" N., long. 9316'00" E.); 

 1,040 meters; bottom temperature 4.44 C.; green mud and foraminiferal ooze; Investi- 

 gator [A. H. Clark, 1909, 1912, 1916, 1918; Gislen, 1934] (1, I. M.). 



History. Pachylometra invenusta was originally described in 1909 from a single 

 specimen dredged by the Royal Indian Marine Survey steamer Investigator off South 

 Andaman Island. It was redescribed and figured in 1912. On the establishment of 

 the genus Perissometra in 1916 invenusta was transferred to it. In my memoir on the 

 unstalked crinoids of the Siboga Expedition published in 1918 invenusta was included 

 in the key to the species of the genus Perissometra and the synonymy and locality were 



