2 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



ability, all attempts to correlate these fossil forms with their recent represent- 

 atives can be little else than pure guesswork. 



Unfortunately, I have not been able to examine the radial pentagon of 

 nearly so many species as I would have wished, nor have I been able to examine 

 large series of specimens except in a very few instances, and it has therefore 

 been impossible for me to arrive at many conclusions of a real and permanent 

 value. A great many facts have been brought out, however, which show the 

 importance of this line of work, especially in its bearing upon the fossils, and 

 it is greatly to be hoped that every student of the comatulids (as well as of the 

 stalked types) will seize every opportunity to make dissections of such species as 

 may be available so that data may gradually accumulate whereby the true system- 

 atic importance of the various features of radial joint face sculpture may prop- 

 erly be appreciated. 



It has seemed best to unite in one place the detailed descriptions of the radial 

 articular faces of all the species which I have been so fortunate as to be able 

 to examine. This will render them much more readily comparable with each 

 other than if the descriptions were incorporated with the general descriptions 

 of the species, and at the same time will facilitate their use in connection with 

 the fossils. Furthermore, for purposes of identification and determination the 

 external characters are the ones upon which reliance is chiefly placed, and it 

 seems therefore inadvisable to burden the systematic descriptions with a do- 

 tailed account of internal structures. I have included, however, in the descrip- 

 tion of each species of which I have been able to examine the radial pentagon 

 a synopsis of its salient features in order to indicate the correlation between 

 these internal and the more familiar external characters. 



The most generalized type of radial articular face, and that toward which 

 the radial articular faces of all young specimens converge, consists of a large, 

 deep, semicircular dorsal ligament fossa, in the middle of the anterior (ventral) 

 border of which, just under the transverse ridge, there is a circular or transversely 

 oval, usually somewhat sudden, excavation, known as the ligament pit, which 

 may involve a portion of the proximal (dorsal) side of the transverse ridge in 

 its formation; beyond the middle of the transverse ridge, which is high, is the 

 large opening of the central canal, surrounded by a raised calcareous platform 

 on a level with the transverse ridge which is continued laterally so as to form 

 a ventral border to the ridge; on either side of the central canal lie the inter- 

 articular ligament fossae, which are typically isosceles triangles with their bases 

 resting on the transverse ridge: beyond these are the large distally rounded 

 muscular fossae, the area of which is at least as great as that of the interarticular 

 ligament fossae; these are separated interiorly from each other by a high narrow 

 ridge joining the platform about the central canal (which is raised so high 

 above the lower apices of the muscular fossae that the central canal appears to 

 lie in a sort of tube or tunnel) which decreases in height, at first very rapidly 

 but later more gradually, until distally it sinks to the level of the adjoining 

 fossae; a slight notch separates the distal edges of the muscular fossae interiorly. 



