186 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Diagnosis. — A genus of Thalassometridac in which the third-fifth segments of the 

 genital pinnules are greatly expanded, forming a roof over the gonads; there are 10-22 

 arms with all the division series 2; and the cirri are arranged in 10 columns on the 

 centrodorsal. The single included species is small and delicate, with the arms up to 50 

 mm. in length. 



Geographical range. — From northern Cuba eastward and southward along the An- 

 tillean chain to St. Vincent and ?Grenada. 



Bathymetrical range. — From 159 to 479 meters. 



Thermal range.— From 8.3° to 16.67° C. 



History. — -The only known species of this genus was first mentioned as Antedon 

 duplex by Prof. Ludwig von Graff in 1883, this name having been furnished him by 

 Dr. P. H. Carpenter, who later used it in his report upon the comatulids of the Challenger 

 expedition published in 1888. In my first revision of the old genus Antedon published in 

 1907 duplex was referred to the new genus Thalassometra. In my revision of the family 

 Thalassometridae published in 1909 I included Antedon duplex in a list of species which 

 I was unable to place satisfactorily. In my report upon the unstalked crinoids of the 

 Siboga expedition published in 1918 I included the new generic name Horaeometra in 

 a key to the genera of the subfamily Thalassometrinae, and under this name I listed 

 Horaeometra duplex, with its synonymy. At the same time I included the new specific 

 name koehleri in the key to the species of the genus Cosmiometra, giving as the range 

 St. Vincent, in 158 meters; C. koehleri subsequently proved to be based upon a specimen 

 of H. duplex. Since 1918 the status of the genus Horaeometra has remained unchanged. 



HORAEOMETRA DUPLEX (P. H. Carpenter) 



Plate 6, Figure 24 

 [See also vol. 1, pt. 2, fig. 321, p. 227.] 



Antedon duplex von Graff, Bull. Mus. Comp. Zool., vol. 11, No. 7, 1883, p. 133 (nomen nudum; off 

 St. Vincent, 124 fins.; myzostomes). — von Graff, Challenger Reports, Zoology, vol. 10, pt. 

 27, 1884, pp. 17, 18, 75 {nomen nudum; Blake station 269; myzostomes). — P. H. Carpenter, 

 Challenger Reports, Zoology, vol. 26, pt. 60, 1888, p. 54 (specific formula), p. 207 (10-armed 

 Blake species), p. 208 (both 10-armed and multibrachiate), p. 211 (myzostomes), p. 212 (in key 

 to the species of the Spinifera group), p. 217 (compared with [Stiremetra] lusitanica), pp. 367, 368 

 (bathymetrical range), pp. 375, 378 (Caribbean islands and Straits of Florida, 88-262 fins.). — 

 Hartlaub, Bull. Mus. Comp. Zool., vol. 27, No. 4, 1895, p. 130 (systematic and bathymetrical 

 relationships), p. 135 (compared with A. [Thalassometra] agassizii). — Minckert, Archiv Naturg., 

 Jahrg. 71, 1905, vol. 1, Heft 1, p. 211 (syzygies; arm division). — Hamann, Bronn's Klassen 

 und Ordnungen des Tier-Reichs, vol. 2, Abt. 3, 1907, pp. 1578, 1581 (listed). — A. H. Clark, 

 Proc. Biol. Soc. Washington, vol. 22, 1909, p. 18 (not placed in a revision of the Thalassometri- 

 dae).— Hartlaub, Mem. Mus. Comp. Zool., vol. 27, No. 4, 1912, p. 280 (in the Blake collection), 

 p. 309 (in the Spinifera group; history), pp. 366-370 (Blake stations 232, ?249; detailed descrip- 

 tion and discussion), pi. 3, figs. 2, 4-11, pi. 14, figs. 5, 10, 13. 



Thalassometra duplex A. H. Clark, Smithsonian Misc. Coll., vol. 50, pt. 3, 1907, p. 360 (listed). 



Cosmiometra koehleri A. H. Clark, Unstalked crinoids of the Siboga-Expcd., 1918, p. 154 (in key; 

 range; based on Antedon duplex Hartlaub [parti, Mem. Mus. Comp. Zool., vol. 27, No. 4, 1912, 

 p. 366, pi. 3, figs. 2, 4; pi. 14, figs. 5, 10). 



Horaeometra duplex A. H. Clark, Unstalked crinoids of the Siboga-Exped., 1918, p. 160 (references); 

 The Danish Ingolf-Expcd., vol. 4, No. 5, Crinoidea, 1923, p. 40 (range). — H. L. Clark, Mem. 

 Soc. Cubana Hist. Nat., vol. 15, No. 1, May 1941, p. 9 (Atlantis stations 2999, 3303, 3437, 3465, 

 3466, 3467, 3478, 3479, 3480; off the north coast of Cuba, about 100 fathoms). 



