110 



BRITISH PALEOZOIC ASTEROZOA. 



first-named species is the more primitive. The appearance towards the distal 

 extremity of the arms is similar in both species and highly characteristic. Both 

 adradialia and supero-marginalia if seen in slight profile view, look half-moon- 

 shaped. This is well seen in the case of U. hinahani in the lower left-hand side of 

 PI. V, fig. 4, and in U. ramseyensis in Text-fig. 64. Many of the infero-marginalia 

 have distinct swellings, each of which carried a long prominent spine. Schnchert 

 notes that the distal infero-marginalia of P. specwsus also tend to become strongly 

 convex with " one prominent point for an articulatory spine " (1915, p. 143). This 

 is a further point which enables one to link up an English Uranaster with the 

 American J', speciosus. The infero-marginalia of U. kinahani appear to be much 

 flatter, and I have not been able to recognise prominent spines with certainty. 



65 



GG 



—MP 



5.M. 



m. 



Text-pig. 65. — Wash drawing of a portion of the oral surface of Uranaster ramseyensis (L. 11036 6) to 

 show the disc. I.M., infero-marginalia; M.P., month-angle plates; S.M., supero-marginalia; V.L., 

 ventro-lateralia. x 7. 



Text-fig. 66. — Wash drawing of a portion of the oral surface of Uranaster ramseyensis (L. 11036 a) to 

 show the ambulacra! groove. Ad., adambulacralia ; Am., ambulacralia ; I. M., infero-marginalia. x 5. 



Oral Surface (Plate VI, figs. 1,3; Text-figs. 65, 66). — So far as it can be made 

 out, the oral aspect is almost precisely that of U. kinahani, except that the 

 adambulacralia outnumber the infero-marginalia. Unfortunately, there is no good 

 view of the interior of the interbrachial region of the disc or of the mouth-parts. 

 The drawing given (Text-fig. 65) shows that some ventro-lateralia were present, 

 but their exact arrangement cannot be made out. The mouth-angle plates appear 

 to have been large and prominent as in U. kinahani. 



Measurements. — L. 11037 with its counterpart has approximately R : r : : 11 mm. : 

 4 mm. L. 11038 with its counterpart is slightly larger. 



Horizon and Locality. — Hicks supposed that the beds from which these 

 specimens were obtained were of Tremadoc (Upper Cambrian) age. Prof. O. T. 

 Jones, however, in a letter to me, states : " The Ramsey Island Tremadoc beds have 

 been shown by Mr. J. Pringle (' Greol. Mag.,' 1911, pp. 556 — 9) to be in all 



