146 BRITISH PALEOZOIC ASTEROZOA. 



Urasterclla medusa, Hudson. — The structure of the arm, as shown by Hudson 

 (93, pi. 3, fig. 2), suggests that this is a true Urasterella. The only specimen 

 discovered is from the Trenton beds. 



Urasterella ulrichi, Schuchert. — The figures and description given (85, pp. 183— 

 185) leave no doubt that this is a true Urasterella. The species may become very 

 large (R : r : : 78 mm. : 12 mm.). Schuchert states that in the angles between all 

 the apical plates " are left subcircular small openings." These must have been for 

 papulae. The radialia are not in series but are separated by adradialia which have 

 thrust themselves between the plates very much as in Promopalaeaster (Text-fig, 

 52, p. 93) and Uranaster (Text-fig. Gl, p. 106), a suggestion that the lineage to 

 which the species belongs is reaching its maximum of elaboration. The arms are 

 highly convex. Schuchert notes (op. cit., p. 185) that " the best preserved speci- 

 men of U. ulrichi has two nearly full-grown rays and three short stumps. One of 

 these short rays is so well preserved as to indicate that this condition is not due 

 to poor preservation, but is apparently a case of accidental loss of parts during 

 life. The wound has been healed, but no regeneration of lost parts has taken 

 place, as is so common in similar losses among the living starfishes." This account 

 should be compared with that given for regeneration in Cuemidactis (p. 161). 



The specimens are from the Black River (Middle Ordovician) formations of 

 Minneapolis, Minnesota. It is interesting to find such an elaborated form at this 

 early age. 



The following species of Urasterella are mentioned but not described by 

 Clark, J. M. (94, p. 36): U. ruthveni, mut. arisaigensis, nov. ; U. lutheri, n. sp. ; 

 U. stetta, n. sp. ; U. schucherli, n. sp. ; Urasterella, n. sp. 



German Species of Urasterella. 



Urasterella asperula, Roemer. — Schuchert has shown (85, pp. 188-189) that the 

 specimens of this form in the United States National Museum and the Yale 

 Museum belong to species of a true Urasterella. 1 have examined the specimens 

 in the British Museum (Nat. Hist.) figured by Stiirtz as Roemeraster asperula (76, 

 pi. ix, figs. 4, 5). The apical surface shows a very similar structure to U. ruthveni, 

 var. leinhoardinensis. The form is larger, however, than any found in England, 

 and there is a loss of symmetry of the central plates on the apical surface of the 

 disc. I am inclined to regard it as merely a horizon variety of U. ruthveni. 



Specimens are fairly common in the roofing slate of the Lower Devonian of 

 Bundenbach, Germany. 



French Species of Urasterella. 

 Schuchert suggests (85, p. 187) that the Asterias constellata of Thorent 



