A MONOGRAPH OF THE EXISTING CRINOIDS 65 



between the genera of Thalnssometridae with carinate arms, all the division series 2, 

 and a scarcely modified PI, and the genera with dorsally rounded arms, the IIBr series, 

 if present, usually 4(3+4), and a much enlarged PI. 



History. The first known species of this genus was described under the name of 

 Antedon compressa by Dr. P. II. Carpenter in 1888. A second species was described 

 as Antedon orion in 1907. In my first revision of the old genus Antedon published 

 later in 1907 compressa and orion, were both referred to the new genus Charitometra, 

 but in a paper published on April 11, 1908, I said that "the species compressa and 

 orion, placed in Charitometra, should have been referred to Thalassometra." Later in 

 the same year (May 14) I described Thalassometra Jisheri. In my revision of the family 

 Thalassometridae published in January 1909 I established the genus Parametra with 

 the genotype Antedon orion A. H. Clark, 1907, including in the new genus compressa, 

 fishcri, and orion. Parametra granulata was briefly diagnosed in 1913. 



In discussing the specimens of Parametra granulata and P. compressa hi the British 

 Museum in 1928 Prof. Torsten Gislen said that the genus Parametra must be referred 

 to the Charitometridac, under which family he placed it. In 1934, however, he revised 

 this opinion. 



KEY TO THE SPECIES IN THE GENUS PARAMETRA 



a 1 . Arms carinate or subcarinate, at least with a low but distinct carinate line, never evenly rounded 



dorsally; cirri with the transition segment the eighth; PI evenly tapering. 

 b 1 . Distal cirrus segments broader than long with prominent carinate processes; cirri about one-fifth 



the arm length. 

 c 1 . Not more than 20 cirrus segments; usually 15-20 arms. 



d 1 . Lateral portions of the division series and arm bases smooth; 15-20 arms 120-140 mm. 

 long; cirri 23 mm. long with 16-20 segments (from the Timor Sea to the Kei Islands and 



north to Halmahera; 216-795 meters) compressa (p. 65) 



d*. Lateral portions of the division series and arm bases more or less covered with fine tubercles; 

 12-20 (usually 17-20) arms 145-170 mm. long; cirri with 18 segments (Philippine Islands; 



150-510 meters) granulata (p. 69) 



c 2 . Cirrus segments 20-25 in fully developed individuals; usually 10-15 anna 125-140 mm. long 

 (Hong Kong to southern Japan from the Korean Straits to Sagami Bay; 128-306 meters). 



orion (p. 72) 



b 1 . Distal cirrus segments as long as broad with very small and obscure dorsal processes; cirri 

 about one quarter of the arm length; 19 arms 115 mm. long, the cirri 20-28 mm. long with 



25-26 segments (Kei Islands; 250 meters) lisa (p. 83) 



of. Arms evenly rounded dorsally, the brachials with prominent or thickened distal ends; Pj more 

 or less swollen basally, not much longer than the more slender and evenly tapering P 3 ; cirri 

 rather long and stout, about one quarter of the arm length, with the transition segment from 

 the fifth to the eighth. 



&'. Outer cirrus segments with a rather high transverse ridge with the crest flattened and dentate, 

 on the last six becoming a low subrnedian dorsal tubercle; transition segment the sixth, seventh, 

 or eighth; 20 arms about 90 mm. long; cirri 20-25 mm. long with 23-27 segments (Malay 



Archipelago) ajax (p. 84) 



b 2 . Outer cirrus segments with prominent and sharp dorsal spines; transition segment the fifth; 

 13 arms 110 mm. long; cirri 20-25 mm. long with 19^-26 segments (Hawaiian Islands; 351- 

 643 meters) fisheri (p. 86) 



PARAMETRA COMPRESSA (P. H. Carpenter) 



PLATE 8, FIGURE 26 



Antedon compressa P. H. CARPENTER, Challenger Reports, Zoology, vol. 26, pt. 60, 1888, p. 222 

 (description; Challenger station 192 [the specimen from station 201 = P. granulata]), pi. 41, figs. 

 84380350 6 



