Clark — A Revision of Thalassometridas and Himerometridfe. 3 



I have used great care in the selection of the types of the 



new genera described herein. The types are, wherever possible, 



the first species to have been described, and the commonest 



species ; but in cases where the original descrii^tion is deficient, 



or the identification doubtful, I have taken one of the later species, 



where circumstances permitted one considered as a synonym 



of the first described. Preference has always been given to 



species at hand to guard against the possibility of nomenclatorial 



disturbance through misconception of species not personally 



known to me, as so much trouble^ has arisen in other groups 



because of certain species being supposed by authors to be one 



thing, but on examination proving to be something quite 



different. 



Family HIIMEROMETRID.E. 



KEY TO THE INCLUDED GENERA. 



a} Pi greatly elongated, l\ and following pinnules extremely short, only 

 about one-fifth as long as Pi ; cirri long and stout, with about 80 

 joints; anal tube very long and slender; rays rounded and very 

 widely separated (1) Pontiometra. 



a? P2 resembling Pj equal in size, or larger; anal tube stout, not espec- 

 ially long; rays never very widely separated. 

 /)' no pinnule on the fourth (epizygal) brachial (i. e., Pa al)sent). 

 c^ cirri long with more than 35 joints ; all the pinnules long and stiflF, 

 none of the proximal pinnules greatly longer than the others 



(2) Colobometra. 

 c^ cirri short, with less than 30 joints; distal pinnules soft and deli- 

 cate; one or two of the proximal pinnules much larger and 

 stifFer than the others (3) CyUometra. 



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

 c^ middle and distal Ijraehials extremely short and oblong; i Br and 

 lower brachials strongly convex dorso-ventrally, appearing 

 swollen. 

 d} I Br and first two brachials in apposition for their entire length ; 

 synarthrial tubercles strongly developed ; Pj smaller and more 

 slender than P, ; 10-20 arms (4) Amphimetra. 



d'^ I Br and division series rounded, and widely separated laterally; 

 synarthrial tubercles not developed; Pi resembling P^ and 

 Pp and larger than P2 ; more than 25 arms (5) Himerometra. 

 c'^ middle and distal Ijraehials wedge-shaped or triangular, not par- 

 ticularly short; i Br, further division series, and lower brachials 

 not swollen. 

 d^ 10 arms; cirri short and stout, the component joints sub-equal, 

 usually squarish, sometimes broader than long; opposing spine 

 median, erect; joints of lower pinnules with more or less devel- 

 oped keels or lateral processes (6) Oligometra. 



