STRATIGRxVPHICAL DISTRIBUTION. 



33 



pentagon, being made up of straight pieces; in some others they arc arched, and give an 

 ogive form. 



Locality. — Leintwardino, abundant of all sizes in Lower Ludlow Rock. 



Proiaster /eptosonia, Salter. 'Ann. and jMag. of Nat. Hist.,' 2d series, vol. xx, p. 331. 



pi. ix, fig. ."). 



Disc thin, membranous, seldom preserved ; arms slender, one inch long ; oral 

 pentagon conspicuous, of a beautiful petaloid shape, constructed, according to Mr. Salter, 

 of a series of ogives, the salient angles of which are inserted into the base of the arms 

 and formed of three pairs of bones, Avhile in P. Miltoni only two are distinct, and these 

 are set in an angular form (fig. 17, c). Small spines are fixed to their extremities. 



Localifi/. — Leintwardino in Lower Ludlow Rock. 



Proiaster SedpoicJcii, Forbes. ' Mem. Geo!. Surv.," dec. i, pi. iv. 



" The upper and under surfaces of the disc were covered by small, similar, more or less 

 regular, polygonal or crescentic plates, imbricated in scale-fashion, and having punctated 

 surfaces. Those of the under side of the l^ody are smaller and more regular than those of 

 the upper. The mouth is central, and rather small in proportion to the disc. The buccal 

 apparatus is composed of ten parts or processes, arranged in pairs ; half of each springs 

 from the origin of each arm in a diverging manner, and meets the corresponding half to 

 form a lanceolate, tooth-like projection, deeply indenting the cavity of the mouth. The 

 arms were composed of alternating sonievv'hat quadrate ossicula, the sides of which were 

 deeply indentated superiorly, in order to form spiniferous crests. The spines were short, 

 not equalling the length of an ossicle, obtuse, and few in a row ; anibulacral grooves wide 

 and convex; the central pentagon very deeply cut, of live oval, pointed petals. 



Locality. — Underbarrow, Westmoreland, in Lower Ludlow Rock. 



Protaster Salteri, Sow. ' Quart. Jour. Geol. Soc.,' vol. i, p. :2(). 1845. 



Discovered by Professor Sedgwick and Mr. Salter many years ago in Lower Silurian 

 rocks, near Cerrig-y-Druidion on tlie Holyhead road ; the original specimen has un- 

 fortunately been lost. 



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