112 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



is doubtless of very similar nature to those that have brought about 

 an eleutherozoic habit on the part of other crinoids. It is for this 

 reason that these forms have been introduced in the present paper. 



Edriocrinus. — The genus Edriocrinus has long been known, although 

 its genetic affinities are but poorly understood. It has a fairly long 

 geologic range, being found from the New Scotland to the Onondaga. 

 Its structure is apparently very simple, as will be seen by reference to 

 Plate 11, figures 1, 2, 9, 14, 15. The cup consists of five radials and 

 an anal plate. The latter is somewhat narrower than the radials 

 but of equal height. This cup rests upon an apparently amorphous 

 base. The arms are short but remarkably broad and stout, indicating 

 adaptation perhaps more to a shallow water habit than to an eleu- 

 therozoic existence. The shape of the base and the relation of the 

 thecal plates to it vary considerably. This variation is immediately 

 obvious in a comparison of Plate 11, figures 1 and 9. 



Edriocrinus dispansus, new species (PI. 11, figs. 1 and 2), offers 

 perhaps the most interesting variant from the normal Edriocrinus 

 structure. In this species, which occurs in the Linden ( Helderbergian) 

 of Big Sandy River, Benton County, Tennessee, the base is greatl}'' 

 expanded. In the specimen here figured the animal is attached to a 

 shell of Leptdenxi rhomhoidalis, which it entirely covers and extends 

 beyond. Despite the great expanse of the lower portion of the cup, 

 the diameter of the theca at the arm bases is comparatively small. 

 It is to be noted that the radials and anal are directed inward, rather 

 than vertically or outward, as in the case of most Crinoidea. As a 

 result the radials are considerably broader at the base than at the top. 

 There is no other species of Edriocrinus that in any way approaches 

 tliis form. The holotype of this species is in the United States 

 National Museum. (Cat. No. 27757.) 



As going to the opposite extreme from Edriocrinus dispansus 

 should be taken E. pyriformis. In tliis species (PI. 11, fig. 9) the 

 peduncle is comparatively slender and elongate, having more the 

 appearance of a short, fairly stout column. The other species of 

 Edriocrinus lie intermediate between this and the preceding species, 

 both structurally and geologically. 



Edriocrinus sacculus, from the Oriskany, is a type that offers many 

 interesting features relative to the structure of the genus. It is 

 through the evidence of this form, for instance, that we know anything 

 in regard to the structure of the arms of Edriocrinus. This species 

 Hkewise combines an eleutherozoic and statozoic habit. The species 

 is constantl}^ attached in the young forms, as may be noted in Plate 

 11, figure 14. The young apparently were often associated in groups 

 or clusters as here indicated. A number of these clusters have been 

 noted where the young are cemented to brachiopod or gastropod 

 shells. In certain individuals it appears that attachment was main- 



