MESOPAL^ASTER (?) LEINTWARDENSIS. 89 



the most proximal plate of the adambulacral series is obviously composed of a 

 fused mouth-angle plate and a first adambulacral. This complication of the mouth- 

 parts is a distinct approximation to that found in Promopalxaster, and shows the 

 racial affinity of the two genera. 



The plates of one of the interradial angles of the second specimen on D. 74c are 

 slightly displaced, and show that there is a distal prolongation of the odontophor 

 which fits in between the first infero-marginalia. This prolongation is usually 

 hidden from view. 



The specimen in the British Museum is interesting inasmuch as the odonto- 

 phor is considerably larger than in the Thraive Glen specimen, and is not 



Text-fig. 48. — Wash drawing of the mouth-parts of Mesopalceaster complicafus (taken from 



D. 74). X 16. 



completely enclosed by the proximal infero-marginalia. In this respect the form 

 is in the " tludsonaster^' stage. A row of very distinct intermarginalia is present, 

 and there can be no doubt that the form belongs to the species under description. 



Ornament. — Of a rather coarse pustulose type. 



Measurements. — R : r : : 8*5 mm. : 2*4 mm. Width of arm at base is 2*5 mm. 



Horizon and Locality. — Upper Ordovician (Ashgillian) of Girvan, Ayrshire, 

 Scotland. 



3. MesoDalseaster (?) leintwardensis, n. sp. Plate II, fig. 5; Text-fig. 49. 



Material. — One specimen only is known of this species, an imprint in the 

 British Museum (Nat. Hist.), No. E. 13153. 



Spea'iic Characters. — A small form with broad obtuse arms. 



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