4 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



recognize. The species of Parametra, which have relatively short and stout cirri with 

 few segments, bear considerable superficial resemblance to some of the species of the 

 family Charitometridae, but the cirri have an exceptionally well-marked transition seg- 

 ment beyond which the segments are light in color with a polished surface and bear 

 dorsal processes, and PI, though not greatly enlarged, is longer than P 2 . In Leilametra 

 the cirri are very long and straight with numerous (up to 83) segments which do not bear 

 dorsal processes; but PI is long and basically enlarged as in related genera. 



The 14 genera included in the family Thalassometridae fall into three distinctive 

 groups. In the first group, consisting of the genera Stenomctra, Daidalometra, Stylo- 

 metra, Cosmiometra, Parametra, and Lissometra, the arms are strongly compressed lat- 

 erally and are sharply carinate, at least in the outer portion, and are always, except for 

 individual variants in the genera Daidalometra and Parametra, more than 10 in number 

 with all the division series 2; PI resembles P2, but is longer and proportionately stouter. 

 This group ranges from southern Japan and the Bonin and Hawaiian Islands to Queens- 

 land and westward to Ceylon and the Maldive Islands, and is represented by the genus 

 Stylometra in the Caribbean Sea; it occurs in water of from 22 to 795 meters in depth. 

 Four of the six genera (Stenometra, Daidalometra, Parametra, and Lissometra) are con- 

 fined to the area between southern Japan, northern Australia, and the Sunda Islands. 

 Of the other two, Cosmiometra covers the entire range of the group, occurring in the 

 Hawaiian Islands, in Bass Strait between Australia and Tasmania, and in the Maldive 

 Islands, with the related Stylometra in the Caribbean Sea. 



In the second group, consisting of the genera Crotalometra, Koehlermetra, Aglao- 

 metra, Stiremetra, Oceanometra, Leilametra, and Thalassometra, the arms are rounded 

 dorsally to the tip and are 10 or more in number, if more than 10 the IIBr series are 

 4(3+4) or both 4(3 + 4) and 2, or by occasional individual variation 2; PI is longer than 

 the pinnules following and is usually much stouter basally with carinate processes on 

 the segments; P 2 may be small and short like the segments following, or it may be inter- 

 mediate in character between PI and PS in the larger species. This group ranges from 

 southern Japan, the western Aleutian and Galapagos Islands and Panama, to Fiji, the 

 Kennadec Islands, and southeastern Australia, and westward to east Africa from Sokotra 

 to the Crozet Islands; hi the Atlantic it is found from Tristan da Cunha to the Bay of 

 Biscay ; it occurs in water of from 55 to 2,925 meters, the usual depth being considerably 

 greater than in the case of the preceding group. Of the 7 genera included in this group 

 two, Thalassometra and Stiremetra, are found practically throughout the entire range 

 of the group; both are confined to very deep water; one, Crotalometra, ranges from the 

 East Indies to southeastern Africa, being represented in the south and east Atlantic by 

 the closely related Koehlermetra; one, Oceanometra, a close relative of Thalassometra, 

 ranges from the East Indies to the Hawaiian Islands; one, Aglaometra, bearing much 

 the same relation to Stiremetra that Oceanometra does to Thalassometra, ranges from the 

 East Indies to the Kermadec Islands; and one, Leilametra, is known only from Lombok. 

 But so little is known about the species of this group that any generalizations based upon 

 the distribution of the various genera would be premature. For instance, no species 

 are reported from the Caribbean Sea where some of the genera are certainly represented. 



The third group, including only the genus Horaeometra, is characterized by the 

 abrupt expansion of the third-fifth segments of the genital pinnules, which form a 



