42 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Diagnosis. A genus of Thalassometridae in which the brachials beyond the basal 

 are laterally compressed and carinate; the divisions series, which are all 2, vary from 

 strongly rounded to more or less flattened dorsally with the dorsal surface of the com- 

 ponent ossicles plain and unmodified, or with the edges everted or bordered with fine 

 spines or bands of fine spines; and the brachial carination is not produced into long 

 overlapping spines. The 20-30 arms are 70-130 mm. long, and the slender cirri are 

 25-50 mm. long with 29-74 segments. 



Geographical range. From southern Japan and the Hawaiian Islands to south- 

 eastern Australia (Bass Strait) and westward to Ceylon, the Maldive Islands, and 

 Saya de Malha. 



Bathymetrical range. From 183 (?128) to 730 (?740) meters. 



Thermal range. From 5.44 to 23.2 C. 



Remarks. The genus Cosmiometra, of which Stylometra is the Atlantic representa- 

 tive, is related to Parametra and Lissometra, from which, however, it appears to be 

 quite distinct. When fully developed the species are easily recognized by their long 

 and slender cirri with numerous segments, combined with the 20 or more arms, all the 

 division series being 2, and the arms being laterally compressed and carinate in their 

 middle and outer portions. 



The 10 species of Cosmiometra fall into two groups. In one of these groups the 

 arms are probably 30 in number in fully developed individuals, one IIBr 2 series being 

 present on each of the two outer sides of each postradial series. This group is known 

 only from the Hawaiian Islands (delicata) and from Ceylon and the Maldive Islands 

 (leilae). The two species of this group are probably not closely related to each other, 

 but instead are of independent origin from the stem type of the other group. In the 

 other group there are normally 20 arms, all the IIBr series being present. In spite 

 of considerable variation in detail from one species to another, the species of this group 

 appear to be quite homogeneous, and, except in the number of arms, they do not differ 

 from the species of the first group. In the Atlantic genus Stylometra the single species, 

 S. spinijera, may have either 20 or 30 arms, but this does not appear to be the case 

 in any species of Cosmiometra. 



History. The first known species of this genus (com/era) was described as an 

 Antedon by Dr. Clemens Hartlaub in 1890, and the second (woodmasoni) was also 

 referred to Antedon by Prof. F. Jeffrey Bell in 1893. To these I added Antedon aster 

 in 1907, later in the same year transferring them all to my new genus Thalassometra. 

 In 1908 I added Thalassometra delicata, Th. crassicirra, and Th. komachi. 



On the establishment of the genus Cosmiometra, with the genotype Thalassometra 

 komachi A. H. Clark, 1908 (= Antedon aster A. H. Clark, 1907), I included in it crassi- 

 cirra, delicata, komachi, and woodmasoni. Later in 1909 conifera was recognized as a 

 member of this genus. In 1915 aster was redetermined as the young of komachi, the 

 latter name therefore falling into the synonymy of the former. Since 1915 the status of 

 the genus Cosmiometra has remained unchanged. 



In the key to the species of the genus Cosmiometra published ha 1918m my memoir 

 on the unstalked crinoids of the Siboga expedition there appears the specific name 

 koehleri, with the locality "St. Vincent, West Indies, 158 meters." This supposed new 

 species, which was never formally described, proved to be based upon a specimen of 

 Horaeometra duplex. 



