A MONOGRAPH OF THE EXISTING CRINOIDS 193 



Persian Gulf; Stiff e's Bank; 33 meters; shells and coral sand; Dr. G. Thorson, 

 April 7, 1937 [Mortensen, 1940; Gisten, 1940] 



Muhlos, Maldive Islands; Prof. J. Stanley Gardiner [A. H. Clark, 1929] (4, 

 B. M.). 



Geographical range. From Kurrachi and the Persian Gulf southward to the 

 Maldive Islands. 



Bathymetrical range. From the shore line down to 33 meters. 



History. This species was originally described by me in 1909 under the name 

 Cyllometra mollis from six specimens that had been collected by the Royal Indian 

 Marine Surveying steamer Investigator probably at Kurrachi. It was redescribed 

 and figured under the name Decametra mollis in my memoir on the crinoids of the 

 Indian Ocean published in 1912. In 1913 I recorded and gave notes upon six specimens 

 from Kurrachi that I had studied in the British Museum in 1910. In 1918 mollis 

 was included in the key to the species of the genus Decametra in my report on the 

 unstalked crinoids of the Siboga expedition. In 1929 I recorded four additional 

 specimens in the British Museum that had been collected by Prof. J. Stanley Gardiner 

 at Muhlos in the Maldive Archipelago. 



In 1940 Prof. Torsten Gislen recorded one specimen from off Kharg Island and 

 50 from Stiffe's Bank hi the Persian Gulf that had been collected in 1937 by Dr. G. 

 Thorson. He said that these specimens corresponded very closely to my descriptions 

 written in 1909 and 1912. 



DECAMETRA BREVICIBRA (A. H. Clark) 



PLATE 25, FIGURE 128 



Colobometra (Prometra) brevicirra A. H. CLARK, Crinoids of the Indian Ocean, 1912, p. 321 (descrip- 

 tion; ?India; compared with C. [P.] chadwicki and with C. [P.] owstoni, and with Oligometra 

 serripinna) . 



Prometra brevicirra A. H. CLARK, Rec. Indian Mus., vol. 7, pt. 3, No. 26, 1912, p. 269 (?India). 



Decametra brevicirra A. H. CLARK, Unstalked crinoids of the Siboga-Exped., 1918, p. 118 (in key; 

 range). 



Diagnostic features. -The cirri are 8 mm. long with 21-23 segments which become 

 nearly or quite as long as broad on the antepenultimate; P 2 is 6 mm. long with 12 or 13 

 segments and is not much longer than P,, which has the same number of segments; 

 the outer segments bear spines at the prismatic angles; P 3 is only about half as long 

 as P 2 and is smooth; the arms are about 35 mm. long. 



Description. The centrodorsal is broad and flat, with the cirrus sockets arranged 

 in a single marginal row. 



The cirri are XIV, 21-23 (usually the latter), 8 mm. long. The majority of the 

 cirrus segments are about twice as broad as long, but in the distal half of the cirri 

 the segments very slowly increase in length so that the antepenultimate is nearly or 

 quite as long as broad. The earlier segments have the distal edge thickened on the 

 dorsal side. On the fifth this production of the distal edge begins to divide, the lateral 

 portions becoming swollen and a notch developing in the crest; on the ninth this 

 interrupted transverse ridge has resolved itself into 2 very small and very sharp 

 tubercles situated side by side which on the fifth segment preceding the penultimate 

 themselves give place to single median dorsal spines. At all points these dorsal 

 processes are practically median ; they are exceedingly minute and very sharp. 



