44 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Bathycrinidae. In this family pinnules are absent from a number of the proximal 

 brachials. The pinnular joint face on the more distal brachials reminds one rather 

 strongly of that in Ptilocrinus. The articulation between the first and second pinnu- 

 lars is a muscular articulation of the usual brachial type. The dorsal ligament is, 

 however, narrow and inconsiderable. The distal pinnule segments are distinguished 

 chiefly by the large and extraordinarily thin lateral processes arising from the body 

 of the pinnule segment itself and embracing the ventral soft parts. 



Comasteridae. Aside from the development of combs, the most characteristic 

 feature of the pinnules hi this family is the enormously strong development of the 

 muscle bundles, which is especially remarkable in view of the weak development of 

 the muscular unions between the brachials. 



The angle that the transverse ridge of the brachial face and that of the pinnular 

 face make with each other varies from about 130 in Comaster to 180 in Comissia and 

 Capillaster. The cavity in which the muscles of the first pinnular are inserted on the 

 brachial is usually not very deep. In the proximal comb-bearing pinnules very 

 strong muscle attachments appear, which occupy the greater part of the surface of 

 the facets of the articulations beyond that between the second and third pinnulars. 

 This speaks in favor of these pinnules being specially adapted for making rapid and 

 powerful movements. In the distal parts of the pinnules, where the combs occur, 

 muscles are developed which are enormously more powerful on the side of the dorsal 

 crest on which the teeth are developed. 



In the distal combless pinnules the muscles are more moderately developed. In 

 the articulation between the third and fourth pinnulars and beyond there appears as 

 usual a small dorsal ligament fossa. 



Zygometridae, Himerometridae, Mariametridae, Colobometridae, and Tropiometri- 

 dae. Except in unusual cases the muscular attachments are everywhere small. The 

 pits in the brachials into which the muscles from the first pinnular are inserted are 

 usually fairly deep, but there are some exceptions, as in Himerometra. Between the 

 second and third pinnulars scarcely any muscular fossae are found in the large proximal 

 pinnules of Himerometra. 



In the very long and flexible PI in Pontiometra andersoni the articulations beyond 

 the one between the second and third pinnulars are provided with large lateral muscu- 

 lar fossae. In the more distal parts of the pinnule, as hi the distal pinnules, the dorsal 

 part of the dorsoventral crest disappears, and we therefore get a more or less dis- 

 tinctly marked dorsal ligament fossa. It must be observed that the lumen in this 

 pinnule is unusually large. We may compare the conditions here with the size of the 

 lumen in the immovable proximal pinnules in Stephanometra. 



Gisle"n remarked that in this connection it may be pointed out that the Macro- 

 phreata, provided with large brachial muscle attachments, have in the same way large 

 nerve lumina in the brachials, and a large central organ for these nerves in the centro- 

 dorsal. Stout dorsal nerves are thus correlated with large muscle bundles and a 

 strong capacity for movement or swimming. 



In Stephanometra the stiff and styliform proximal pinnules differ considerably 

 from the rest of the pinnules in regard to their articulations. The articulation be- 

 tween the first and second pinnulars is, as usual, a muscular articulation, and that 

 between the second and third pinnulars is a pinnular articulation in which, however, 



