212 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



Genus ECHINOSTELLA Sturtz. 



Echinostella STURTZ, Verb. nat. Ver. preuss. Rheinl., etc., vol. 56, 1900, pp. 

 233-235, pi. 3, fig. 11; pi. 4, fig. 12. 



The only specimen has 28 or 29 rays and a greatest diameter of 

 150 mm. Abactinally the rays and the central area of the disk 

 stand out rounded above the remainder of this side of the animal, 

 which is not the case in Palseosolaster; otherwise the two genera aie 

 very much alike. 



GenoJiolotype and only species. E. traquairi Sturtz (citations as 

 above). Lower Devonic of Bundenbach, Germany. 



Genus MED US ASTER Sturtz. 



Medusaster STURTZ, Palseontographica, vol. 36, 1890, p. 229; pi. 31, figs. 34,35; 

 Verb, naturh. Ver. preuss. Rheinl., etc., vol. 50, 1893, pp. 54, 73. 



A form with from 12 to 15 rays. Thought to have relationship 

 with living Solaster. 



GenoJiolotype and only species. M. rhenanus Sturtz (citations as 

 above). Lower Devonic, Bundenbach, Germany. 



Cat. No. 59385, U.S.N.M. 



PALEOZOIC OPHIURIDS. 



A great deal has been written about these animals, but in general 

 the true structure of some of them was not known until very recently. 

 Authors have described these delicate and generally poorly pre- 

 served fossils in such broad terms that a complete restudy of all of 

 the material is required before it can be said that most of the genera 

 or even the species are established. The way has been successfully 

 blazed by Schondorf in Europe, and his methods of study and results 

 need to be applied to the American fossils. It was the writer's hope 

 to do this, but it is now plain that his present duties will prevent his 

 doing so. 



In general it may be said that but few Paleozoic so-called ophiurids 

 are true Ophiuroidea. They are ophiurid-like animals, with open 

 ambulacral furrows, but without the essential characters of the 

 Asteroidea. Nor are they transitional in structure between the 

 Asteroidea and Ophiuroidea. Therefore Schondorf has separated 

 them under the term Auluroidea. It seems to the writer that they 

 originated in the Asteroidea early in the Ordovicic in some crypto- 

 zonian stock near Urasterella, with large and square ambulacralia. 

 (Stenaster and Tetraster are probably true aulurids.) Out of the Aulu- 

 roidea, probably in late Devonic time, arose the true Ophiuroidea. 



The essential differences between the Auluroidea and Ophiuroidea 

 will become plainer to the student after a study of the text and 

 figures presented in this work. 



