130 Clark — New Genera of Unstalked Crinoids. 



joints, and the equality of the two proximal pinnules readily differentiate 

 it. It appears to be possible to distinguish two species, which are, 

 L.celtica (Barrettand McAndrew). L. phalangium (J. Miiller). 

 Hathrometra yen. now 



Genotype. — Alectro dentata Say, 1825. 



Radial faces wedge-shaped, less than once and one-half as long as broad ; 

 muscular fossae triangular, less than twice as long as broad, not separated 

 )>y a notch; the ridge between the muscular and interarticular ligament 

 fossae is strongly oblique. Centro-dorsal conical, the sides somewhat con- 

 vex, thickly covered with small and numerous cirrus sockets, which are 

 closely crowded together, and arranged in more or less definite vertical 

 rows. Cirri slender, with fifteen to forty-five joints, dimorphic, the apical 

 cirri having fewer joints than the peripheral, and being considerably 

 smaller; the proximal cirrus joints are much longer than the distal, and 

 more or less " dice-box shaped " ; the distal are squarish, or rather longer 

 than broad, and the dorsal ends may overlap so as to produce spines; an 

 opposing spine is always present, terminally situated. Radials almost, or 

 quite, concealed; costal axillaries rhombic, almost concealing the flrsl 

 costals, which are short, in the median line; the costals arc rounded dor- 

 sally, and in lateral opposition, though not laterally flattened. Ten arms, 

 with triangular joints proximally, becoming more quadrate distally, 

 always (except in the first few discoidal joints) as long as, or longer than, 

 wide. First pinnule long and slender, twice or three times as long as the 

 second; the following pinnules gradually increase in length; the genital 

 glands are long and fusiform. 



Color. — Dark green, or grayish green, sometimes dotted with white. 



Geographic distribution. — Coasts of New Jersey and Portugal north- 

 ward to the Arctic Ocean, and from the seas west of Greenland eastward 

 to the Barents and Kara Seas. 



Depth. — 25 or less to more than 600 fathoms. 



The characteristic conical centro-dorsal with its numerous crowded 

 cirrus sockets, the great length of the first pinnule and the absence of a 

 notch between the distal ends of the muscular fos.se, these being much 

 broader than in Leptometra, at once distinguish this genus. Hathro- 

 metra contains the following species: 



IT. dentata (Say). H. sarsii ( Dubenand Koren). 



//. prolixa (Sladen). //. tenella (Retzius). 



Iridometra gen. nov. 



Genotype. — Antedon adresline A. II. Clark, 1907. 



Cirri few and short, with ten to sixteen joints, the proximal elongate, 

 the distal shorter, on a discoidal or low-hemispherical centro-dorsal. Ten 

 arms, the joints triangular, about as lout: as wide, becoming elongate dis- 

 tally. First pinnule short, never exceeding, and usually shorter than, the 

 -croud, which does not bear a genital gland. 



Color. — Varied and bright, and usually mottled or banded; brick red, 

 white with purple bands, yellow-brown banded with darker, purple and 

 white, or pinkish. 



