2 Clark — A Revision of Thalassometrido' and Himerometrido'. 



and identified from ordinary museum material ; in many cases, 

 as with the larger divisions, the best characters are found in the 

 musculature, studied from the point of view of skeletal muscle 

 insertions, and in the internal structure of the centro-dorsal ; 

 but it has seemed best to omit a discussion of these features 

 from preliminary diagnoses, though I sliall consider them in 

 detail later, especially in reference to the fossil comatulids, in 

 which often only the centro-dorsal and the radials are preserved. 



The family Thalassometridie falls into two approximately 

 equal divisions, in one of which all the species have short, 

 stout, and smooth cirri, and a slender first pinnule composed of 

 very numerous short joints; and in the other long, compara- 

 tively slender, and spiny cirri, and a stout first pinnule, com- 

 posed of enlarged joints. In the latter the proximal cirrus joints, 

 for a variable distance from the centro-dorsal, are rounded, 

 spineless, and with a dull surface, and usually comparatively 

 dark in color; then comes a "transition" joint, which is 

 similar to those preceding for most of its length, but distally 

 has a highly polished surface, is light in color, and bears a 

 small dorsal spine or tubercle; beyond this " transition " joint 

 the joints are shorter, highly jwlished, and bear dorsal spines, 

 and the cirrus is more slender than in tlu' proximal portion. 

 This group thus appears to have the cirri of the other modified, 

 not by a simple increase in the number of joints, but by the 

 addition of a series of a different type of joint liej'ond the pe- 

 nultimate joint of the former (corresponding to the " transition " 

 joint of the latter). This increased cirrus length is correlated, 

 as is commonly the case among the comatulids, with an increase 

 in the size of the lower pinnules (though here affecting only the 

 first) and the result is an animal of radically different appear- 

 ance. I propose to group the forms with sliort, stout, smooth 

 cirri and slender many-jointed first pinnule together under the 

 designation of Charitometrinse, while those with long, compara- 

 tively slender, spiny cirri, and long and stout first pinnule may 

 be taken as composing the sulvfamily Thalassometrinx. 



This modification of the cirri and lower pinnules is not by 

 any means confined to the Thalassometridie ; it is equally marked 

 in the Zygometrid^e, where it separates Eudiocrinus and Catop- 

 tometra from Zygometra, and, with more or less modification, in 

 certain sections of the Himerometridse. 



