NEW SPECIES OF AMERICAN EDRIOASTEROIDEA 



By R. S. BASSLER 

 Head Curator, Department of Geology, U. S. National Museum 



(With Se\tln Plates) 



In a recent paper entitled " The Classification of the Edrioas- 

 teroidea," ^ the writer presented a revised classification of this division 

 of primitive Paleozoic echinoderms belonging to or closely related to 

 the cystids. Six new genera Vv^ere defined, two of which were based 

 on new species, and it was stated that descriptions of additional new 

 species upon which the classification was in part based were in con- 

 templation. The present paper includes these descriptions, as well as 

 comments on and illustrations of previously described species. Its 

 main purpose is taxonomic, and these two^ articles present to the 

 student a brief resume of all genera and most of the species of 

 the class. There is still need for further studies on the anatomical 

 details of the edrioasteroids, but well preserved specimens are so rare 

 that further progress along this line must necessarily be slow. 



It will be remembered that these primitive echinoderms, ranging 

 from parasitic, circular expansions to elevated, sacklike bodies, free 

 or attached by a part or all of the lower (aboral) surface, bear 

 normally five straight or curved ambulacra (rays or arms) on their 

 upper (oral) surface, arranged as follows: (i) left posterior (next 

 to anal area) ; (2) left; (3) anterior (opposite anal area) ; (4) right ; 

 (5) right posterior. Usually, four of the ambulacra curve to the 

 left (sinistral or counterclockwise), and the fifth (the right posterior) 

 to the right (dextral or clockwise), the anal interradius thus occurring 

 between the right and left posteriors. However, in some genera the 

 rays are straight, or, again, they may all curve to the left or all to 

 the right, or, as in the first established genus, Agclacrinites, three 

 to the left and two to the right. Study of many specimens has shown 

 that the direction and extent of curvature of the ambulacra, as well 

 as the plate structure of the rays, the interradii or interambulacral 

 areas, and the oral area, remain constant for the genus, but the number 

 of ambulacra, although typically five, may vary in the same species 

 just as in the modern starfishes. 



^Smithsonian Misc. Coll., vol. 93, no. 8, pp. i-ii, i pi., 1935. 



Smithsonian Miscellaneous Collections, Vol. 95, No. 6 



