74 



BRITISH PALEOZOIC ASTEROZOA. 



Measurements. — R : r : : 16*5 mm. : 4*5 mm. Width of arm at base is 5 mm. 

 There are fifteen supero-marginalia, and seventeen infero-marginalia. 



Horizon and Locality. — Upper Ordovician (AshgilHan) Starfish bed at Girvan, 

 Ayrshire, Scotland. 



A specimen (E. 13532) from the collection of T. Ruddy in the British Museum 

 (Nat. Hist.) is apparently the oral side of B. ordomcus. I hesitate, however, to 

 assign it to this species, as the holotype and this specimen were obtained from 

 such widely different horizons. 



36 



37 



Text-fig. 36 (on left).— Plan of the apical surface of one arm and the margin of the disc of Belaster 



ordoviciis (based on D. 44). x 6. 

 Text-fig. 37 (on right). — Plan of the oral surface of the greater jmrt of an arm and the disc of Belaster 



orrfoBicM.9 .? (based on E. 13532). x 6. 



Description (Plate III, fig. 4; Text-fig. 37). — The odontophor is long and 

 narrow. Its proximal side is wide and rounded, the sides bordering the infero- 

 marginalia are indented, whilst the distal side is short and almost straight. 

 The proximal pair of infero-marginalia are large. Each is widely separated by 

 the odontophor from the corresponding infero-marginal of the neighbouring arm. 

 The second pair of infero-marginalia are distinctly smaller than the first pair, but 

 from this point there is little differentiation in the series. The mouth-angle plates 

 are very conspicuous. The base which fits on the odontophor is slightly shorter 

 than the base of the proximal adambulacralia, but the plate widens considerably 

 proximalwards, and projects well into the mouth- cavity. The adambulacralia are 



