142 BRITISH PALAEOZOIC ASTEROZOA. 



Side View.—- There appear to be about thirteen adambulacralia to the first nine 

 infero-marginalia. They seem to retain this proportion (about three to two) 

 throughout the greater part of the length of the arm. This is most clearly seen 

 in a/921, where one of the arms shows a side view of all the regions except the 

 extreme tip. Twenty-three infero-marginalia can be counted occupying the same 

 length as thirty-four adambulacralia. 



Cross- Section. — One of the arms of the holotype has not been fully exposed, and 

 in consequence a mould of a cross-section about half-way along its length is visible. 

 The apical surface is rounded (and perhaps ridged), but it is not tumid as in 

 Salteraster asperrimus. 



Measurements. — 



a/920 (the holotype) R : r : : 27 mm. (approx.) : 2*5 mm. 



Width of arm at base is 2*5 mm. 

 a/921 R : r : : 19 mm. : 2 mm. 



Width of arm at base is 2 mm. 

 a/510 Width of arm at base is 2 , 6mm. 

 Bl R : r : : 50 mm. (approx.) : 35 mm. 



Horizon and Locality. — The Bannisdale Slates (Upper Ludlow) of the Lake 

 district of Westmoreland. Professor Marr tells me that all these Westmoreland 

 starfish beds occur at about the same horizon, namely, near the junction of the 

 Bannisdale Slates and Kirkby Moor Flags. 



Historij.— This species was the earliest Palaaozoic starfish to be described. 

 Forbes remarks that it " was discovered by Mr. John Ruthven, in strata of the 

 Ludlow division of Silurian rocks at Scalthwaiterigg, etc." Forbes gives the 

 measurement of the arms five times as long as the disc is broad. This is almost 

 exactly the measurements given here — 2r=5 mm., R = 27 mm. He also states that 

 the largest specimen examined measured 3^ inches (88 mm.) from arm-tip to arm- 

 tip. This must be a specimen unknown to me, for the arms of the Sedgwick 

 Museum specimens, as exposed by Forbes, were not nearly so large. 



No one has described the species since Forbes' time. Schuchert (85, pp. 17G, 

 177), however, saw the relationship between it and the American species of 

 UrastereUa, but as he had no material of the genotype for study he accepted 

 U. grandis as the genotype for the time being. It is clear that Schuchert was 

 right in his recognition of the affinities of the American species. 



2a. UrastereUa ruthveni, var. leintwardinensis, nova. Plate IX, figs. 3, 4; 



Text-fig. 92. 



Matt rial. — There are three moulds of the species, all from the well-known 

 Church Quarry at Leintwardine. One mould is in the Ludlow Museum, a second 



