URASTERELLA. 147 



(96, p. 250, pi. 22, fig. 7) may belong to Urasterella. He remarks: "The original 

 figure of this species does not permit of determining its generic position. It is 

 described as having but one range of plates on each side of the ambulacra] grooves, 

 and the figure seems to indicate the presence of a large disc with well-defined 

 interbrachial arcs. It seems to have more of the characters of Urasterella than of 

 any other genus. The specimen was found in the Siluric (? Lower) strata in 

 Northern France (Mondrepuis, L'Aisne)." 



Scandinavian Species of Urasterella. 



The Mineralogical Museum at Copenhagen contains a specimen which is almost 

 certainly of U. ruthveni, var. leintwardinensis. It shows the oral surface and 

 presents the same characters as U. ruthveni, and is from the Silurian (Wenlock) 

 of Wisby, Gotland. It is registered as No. 231. I am indebted to Dr. Bather for 

 permission to investigate this specimen, which Avas lent to him. Measurements give 

 R : r : : 22 mm. (approx.) : 2'5 mm. 



Russian Species of Urasterella. 



The Russian Carboniferous species described by Schondorf (65, pp. 323-327, 

 pi. xxiii, fig. 1 ; pi. xxiv, figs. 20-22) under the name of Palseaster viontanus 

 (Stschurowsky) is undoubtedly nearly related to Urasterella. This was recognised 

 by Schuchert (85, p. 180) who named the species Urasterella monta,na. There is 

 a well-preserved specimen of the form in the British Museum (Nat. Hist.) registered 

 as E. 3806. I have investigated it, and make the species have the following 

 diagnostic characters : General arrangement of the plates in cross-section of the 

 arm as in U. ruthveni. Paxilla-shafts shaped like an inverted cone with a flat 

 broad top. Infero-marginalia with ridge-like paxilla-shafts. Ambulacralia much 

 reduced. 



The following notes on the structure add somewhat to our previous knowledge. 



That the species is a Urasterella is shown by the cross-section (Text-fig. 03). 

 The adambulacralia have the usual " Urasterellid " form, and the apical plates are 

 paxilliform and have the Urasterella arrangement. This cross-section differs con- 

 siderably from that figured by Schondorf [op. cit., pi. xxiv, fig. 22). I cannot 

 reconcile the high swollen form and thin ossicles of that figure with the appear- 

 ance presented by the British Museum specimen, or with that which one would 

 expect for a species of the Urasterellidas. 



The adambulacralia are as figured by Schondorf {op. cit., fig. 22 a). He does 

 not appear, however, to have noticed the " Urasterellid " ridge which is low but 

 distinctly visible. At least one long spine which must have articulated with the 

 ridge is present. 



