138 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



pinnules; the cirri are recurved distally, the outer segments with dorsal carinate spines; 

 the arms are 17-28 in number, the division series and arm bases beset with spines, at 

 least along their edges; and one or both of the elements of the pairs in the division series 

 and first two brachials bear a median carinate process. The arms are 1 10-180 mm. long, 

 and the cirri are 40-85 mm. long with 48-79 segments. 



Geographical range. From Timor and the Kei Islands to the Philippines and 

 Hawaiian Islands. 



Bathymetrical range. From 55 to 786 (?872) meters. 



Thermal range. From 4.4 to 12.4 C. 



Remarks. The species of Oceanometra are closely related to those of the genus 

 Thalassometra, from which they differ only in the greater number of arms; in the oc- 

 currence of keels on one or both the elements of the pairs of ossicles in the division 

 series and first two brachials; and in having P 2 intermediate in character between PI 

 and P 3 instead of small and similar to the following pinnules. For the most part they 

 are larger and stouter than the species of Thalassometra, though one of the latter, 

 Th. agassizii, is of equal size. Only one species, 0. annandalei, is known from any 

 considerable number of specimens; of the other two, 0. gigantea is known only from 

 the type specimen, and 0. magna from the type specimen and one other. 



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

 Thalassometra gigantea in 1908. In 1909 a young individual of 0. annandalei from 

 Albatross station 5116 was recorded under the name of Crotalometra eupedata; later in 

 the same year Crotalometra annandalei was described. In 1912 a third species was 

 described under the name of Thalassometra magna. 



The genus Oceanometra was diagnosed in 1916 with the genotype Thalassometra 

 gigantea A. H. Clark, the other species assigned to the genus being listed as Oceanomtra 

 magna and 0. annandalei. The status of the genus has since remained unchanged. 



KEY TO THE SPECIES IN THE GENUS OCEANOMETRA 



a 1 . The second (but not the first) element in the pairs of ossicles in the division series, and the second 

 (but not the first) brachials, bear a high sharp median keel; 17 arms 180 mm. long; cirri stout, 

 75 mm. long with 48-62 (usually 55-60) segments (Hawaiian Islands; 786-872 meters). 



gigantea (p. 139) 

 a 2 . The first as well as the second element in the pairs of ossicles in the division series, and both the 



first and second brachials, bear median keels. 



6'. No spines on the dorsal surface of the proximal ossicles except along the borders and the crest 

 of the keels; ossicles of the division series with irregularly dentate produced lateral borders; 

 dorsal surface of earlier brachials sparsely spinous; 21-28 arms 120-175 mm. long; cirri large 

 and stout, 60-85 mm. long with 63-74 segments (Arafura Sea to western Timor; 204-305 



meters) magna (p. 1 42) 



b 2 . Dorsal surface of proximal ossicles spinous; ossicles of the division series with smooth lateral 

 borders which are not produced; dorsal surface of earlier brachials more or less densely spinous; 

 19-23 arms 110-160 (usually 110-130) mm. long; cirri more slender, 40-65 mm. long with 

 62-79 segments (Philippines and Malay Archipelago; 55-510 meters) annandalei (p. 144) 



