258 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Venezuela; it is predominantly littoral and sublittoral, though the most wide-ranging 

 species is reported from a depth of 508 meters. The family Thalassometridae is 

 almost cosmopolitan in deep water, though it is not represented, so far as is known, 

 in the very cold waters of the polar seas, on the west coast of America, or on the west 

 coast of Africa south of the Gulf of Gumea; most of the species live m water of con- 

 siderable depth, one descending to 2,926 meters, but a few are foimd m shallow water. 

 The family Charitometridae is represented from southern Japan to the Kermadec 

 Islands and the Sahul Bank and westward to east and south Africa, St. Helena, and 

 the Caribbean Sea; most of the species live in water of considerable depth, and one 

 is known from as great a depth as 2,194 meters. In the superfamily Tropiometrida 

 three of the sLx families (Tropiometridae, Thalassometridae, and Charitometridae) are 

 represented in east and south Africa and in the Caribbean Sea; in the superfamily 

 Mariametrida one of the five families (Colobometridae) is represented by two species 

 in the Caribbean Sea, and three (Himerometridae, Mariametridae, and Colobometri- 

 dae) are represented on the east coast of Africa. 



In the arrangement of the recent comatulids given in Part 3, page 65, the super- 

 family Tropiometrida included the families Tropiometridae, Calometridae, Thalas-. 

 sometridae (with the subfamilies Ptilometrinae and Thalassometrinae), and Charito- 

 metridae. The studies of my friend Prof. Torsten Gisl^n have indicated the advisa- 

 bility of raising the Ptilometrinae and Thalassometrinae to family rank, and also 

 recognizing the family Asterometridae (previously included in the subfamily Ptilo- 

 metrinae) with the genera Asterometra and Pterometra. 



The interrelationships of the families included in the superfamily Tropiometrida 

 as at present understood are made clear in the following key: 



KEY TO THE FAMILIES IN THE SUPERFAMILY TROPIOMETRIDA 



a". Ventral perisome of the pinnules not protected by conspicuous side- and covering-plates; cirri 



stout, without dorsal processes Tropiometridae (p. 259) 



a 2. Ventral perisome of the pinnules protected by well developed and conspicuous side- and covering- 

 plates easily visible with a hand lens. 

 b'. Pi very delicate, weak, and flexible, with the first two segments enormously enlarged, those 

 following small and about as long as broad; P2 and usually also one or more of the following 

 pinnules much elongated, enlarged, and stiffened, composed of much elongated segments; 

 disk globose, compact, entirely enclosed in a pavement of plates and readily detached. 



Calometridae (p. 346) 

 h^. Pi not delicate or weak, its first two segments not noticeably enlarged; Pa like the following 

 pinnules, more rarely like Pi, never especially distinguished; disk sunken within the divi- 

 sion series or arm bases with the ventral surface concave, flat, or slightly convex, more or 

 less thickly studded with isolated plates. 

 c'. Cirri usually long and slender, rarely of moderate length and rather stout, composed of 

 more than 25 segments of which the distal are usually much shorter than the proximal, 

 broader than long, and bear prominent dorsal spines or carinate processes; a well-marked 

 transition segment usually present, beyond which the segments have the surface light in 

 color and highly polished, 

 d'. Pi similar to P2, but shorter and smaller; cirri exceedingly long, from nearly as long as 

 to longer than the arms, 

 e'. Centrodorsal large and broad, discoidal or columnar, the numerous cirri closely crowded 

 and irregularly distributed, though tending to arrange themselves in 15 columns; 



radial areas of the centrodorsal never differentiated Ptilometridae (p. 393) 



e'. Centrodorsal a short more or less pentagonal column with a conical apex, the com- 



