148 BRITISH PALEOZOIC ASTEROZOA. 



The ambulacralia are as described by Schondorf, small and strongly compressed 

 in a proximal-distal direction. They differ considerably from those of the pre- 

 viously described species of Urasterella, and resemble in cross-section more the 

 ambulacralia of Galliasterella mira (Text-fig. Ill, p. 167). 



The proximal infero-marginalia have a distinct ridge instead of the usual 

 spine-like paxilla-shaft. The paxilla-shaft of the remaining apical plates is stout 

 and shaped like an inverted cone. Small granular spines seem to have fitted on to 

 the flat top of this cone. These may be, of course, merely the basal remains of 

 original long spines. 



The centre of the apical region was not described by Schondorf. I have been 

 able to expose it, but the exact arrangement of the plates is hidden by the mass of 

 granular spines. 



Text-fig. 93. — Cross-section through an arm of Urasterella monlana. Ad., adambulacral ; I.M., infero- 



marginal ; R., radial, x 15. 



The mouth-parts, as seen in external vieAV, including the odontophor, are 

 exactly as in the described species of Urasterella. Schondorf (op. cit., fig. 21 b) 

 figures them as seen from the ambulacra] groove, and shows no ambulacral corre- 

 sponding to the mouth-angle plates. In the British Museum specimen the mouth- 

 region is sunk, and one cannot expose the plates sufficiently to decide whether this 

 view be correct. The excellent photograph given by Schondorf (op. cit., fig. 1) 

 suggests that the specimen which ho investigated would also not yield good exact 

 views of the groove in the mouth-region. At any rate, his figure is not compatible 

 with any arrangement known in the Urasterellidae. 



The measurements of the specimen described by Schondorf are given as R = 

 (about) 35 mm. ; r = 6-7 mm. The breadth of the arm at about its middle is about 

 6 mm. The dimensions of the specimen in the British Museum are R = (about) 

 22 mm. ; r = 4 mm. The breadth of the arm near the middle is about 6 mm. 



Both specimens are from Mjatschkowa, near Moscow. According to Kayser 

 the beds belong to the lowest series of the Upper Carboniferous (Schondorf, 

 op. cit., p. 326). 



