Clark — A Revision of Thalassometridse and Himerometridae . 5 



SUPPLEMENTARY KEY TO GENERA WITH II BR 2. 



a^ Pi greatly elongated ; P2 and following pinnules extremely short, of 

 uniform length; cirri long and stout, with about 80 joints 



(1) Pontiometra. 

 a^ Pv resembling P, in size, or larger; cirri short, with less than 50 joints. 

 5' no i)innule on the fourth (epizygal) brachial (i. e., Pa absent) 



(3) Cyllometra. 

 b- a pinnule on the fourth (epizygal) brachial (i. e., Pa present), 

 c^ cirrus joints all much broader than long, sub-equal; cirri stout; 

 cirrus spines paired; Po greatly enlarged, the component joints 

 with overlapping and spinous distal ends (7) Cenometra. 



c- proximal cirrus joints longer than the distal, longer than broad ; 

 P2 enlarged, though not greatly diti'erent from one or two neigh- 

 boring pinnules, which may equal or even exceed it ; P2 has 

 smooth joints. 

 d} one or more of the proximal pinnules very stift", straight, sharj)- 

 pointed, and spine-like, though not especially enlarged; i Br 

 and division series with lateral processes 



(9) Stephanometra. 

 d' proximal jjinnules, though enlarged, taper evenly to a slender 

 and delicate tip ; i Br and division series without lateral pro- 

 cesses (11) Dichrometra. 

 1. Pontiometra A. H. Clark. 

 The species belonging to this genus is : 



Pontiometra andersoni (P. H. Carpenter). 



2. Colobometra gen. nov. 

 Genotype. — Antedon perspinosa P. H. Carpenter, 1881. 



Centro-dorsal discoidal, more or less thickened, usually with a slightly 

 concave polar area; cirrus sockets arranged in one, sometimes two, 

 closely crowded, alternating rows. 



Cirri xv-xxv, 35-60, tlie joints with prominent and overlapping distal 

 ends thickly set with fine sjjines; distal cirrus joints about twice as broad 

 as long, always shorter than the proximal, which may be not quite so 

 long as broad to somewhat longer than broad ; prominent dorsal spines, 

 usually paired, developed in the distal half or two-thirds of the cirri. The 

 cirri are equal to ab(jut one-fourth of the arm length. 



Radials visible in the angles of the calyx, but usually concealed in the 

 median line ; i Bri rounded dorsally, entirely separate, decreasing slightly 

 in diameter anteriorly, twice or three times as broad as long; i Br2 pen- 

 tagonal, nearly twice as broad as long to nearly as long as broad; both 

 these joints have slight marginal projections, and are widely free laterally. 



Arms 10; first eight or nine brachials almost oblong, about twice as 

 broad as long, then becoming triangular, about twice as broad as long, 

 then wedge-shaped, though without any especial increase in length until 

 near the extremity of the arm where they become almost as long as broad, 

 though remaining obliquely wedge-shaped. The brachials have projecting 



