256 BULLETIN 8 2, UNITED STATES NATIONAL MUSEUM 



Geographical range. — From Japan, the western Aleutian, Hawaiian, and 

 GaUpagos Islands southward to the Kermadec Islands and Tasmania, and westward 

 to east and south Africa from the Red Sea to the Cape and the Crozet Islands; in the 

 Atlantic from Tristan da Cunha, Ascension, and southern Brazil northward to the 

 Bay of Biscay and the Caribbean Sea. 



Bafhymeirical range. — From the shore line down to 2,926 meters. This super- 

 family is most abundantly represented between 100 and 900 meters, but many species 

 range down to 1,400 meters; one family (Tropiometridae) is almost exclusively 

 littoral, and there are subhttoral or even httoral species in the other families. 



Remarks. — The superfamily Tropiometrida includes the families Tropiometridae, 

 Calometridae, Ptilometridae, Asterometridae, Thalassometridae, and Charitometridae. 

 The families Charitometridae, Thalassometridae, and Asterometridae are closely 

 allied, having most of their characters in common; the family Ptilometridae, the 

 species of which have a close superficial resemblance to those of the family Astero- 

 metridae, differs markedly in the structure of the radial pentagon; the family Calo- 

 metridae is highly distinctive and cannot be confused with any other group ; the family 

 Tropiometridae is equally distinctive, although superficially the included species 

 resemble certain species of Charitometridae. 



Comparisons. — The species of Tropiometridae are all large or very large. The 

 pinnules, though prismatic, are more or less flexible, at least distally, and the side- 

 and covering-plates are minute and rudimentary, represented merely by spicules, or 

 wholly absent. The centrodorsal is large with the cirri arranged in more or less 

 regular alternating rows. The cirri are stout and rather short, without dorsal spines, 

 and rather strongly recurved ; they resemble the cirri in some of the species of Charito- 

 metridae. Very distinctive are the articular faces of the radials on which the muscular 

 fossae are large and well rounded, about twice as high as the interarticular ligament 

 fossae, with their lower inner corners occupied by supplementary muscle plates (see 

 Part 2, pp. 38-40). 



The family Calometridae is rather sharply set apart from the other families of the 

 Tropiometrida. The species are all of medium size. Pi is small, weak, and flexible, 

 with the first two segments greatly enlarged and the remainder about as long as 

 broad. One or more of the pinnules following are elongated and spinelike. The 

 remaining pinnules are sharply prismatic, stiff, with very highly developed side- and 

 covering-plates. The division series and arm bases are less closely appressed than 

 they are in the species of the other families, and are sometimes {Neometra) widely 

 separated. The centrodorsal is moderate, usually thick discoidal, with the cirri 

 arranged in a few more or less irregular rows. The cirri are of moderate length and 

 stoutness, with dorsal spines on the outer segments. The articular faces of the radials 

 are highly distinctive. They are approximately crescentic and are entirely separated 

 from each other. The interarticular ligament fossae have the distal border strongly 

 concave, and the muscular fossae are very short, about as long as the dorsoventral 

 diameter of the central canal, forming a bandlike border along the distal edge of the 

 interarticular ligament fossae (see Part 2, pp. 40-41). 



!-V. ^' The species of Ptilometridae are of moderate size or rather large. The pinnules 

 are prismatic and stiffened with the side- and covering-plates well developed. Pi is 

 smaller and more slender than the pinnules following, though otherwise similar to 



