76 FOSSIL ASTEROIDEA. 



The moutli-angle plates are not pi'ominent. The adambulacral plates possess 

 a triple row of spines. 



Dimensions. — Specimens 35,481 and 40,400. — The greatest -width of the ray 

 varies from 8'3 to 6*5 mm., and the least width from 7'2 to 5"7 mm. The supero- 

 marginal plates are 3'2 mm. broad near the interradii. 



Specimen E. 5038. — Greatest width of ray 10" 5 mm. 



Specimen in Brighton Museum. — Greatest width of ray 9*2 mm. 



Localitj/ and Stratigraphical Position. — Upper Chalk, Lancing, Sussex, and 

 also from the Upper Chalk of Kent. 



PaHuV//— PEXTACEROTID^ {Gray) emend. Perrier, 1834. 



Phanerozonate Asteroids with unequally developed marginal plates, the superior 

 series being frequently masked or hidden in membrane. Abactinal skeleton 

 reticulate. Plates with large isolated tubercles, or spinelets, or granulose, or 

 covered with membrane. Actinal interradial areas with large pavement-like 

 plates which bear unequal-sized granules. 



GenHs— PEXTACEROS, Schidrw, 17G0. 



Pentaceeos, Schuhe, 17G0. Betrachtung der versteinerten Seesteme imd ihrer 



Tlieile, Warscliau u. Dresden, p. 50. 

 GoNiASTER (pars), Agassiz, 1835. Mem. Soc. Sci. Nat. Neuchatel, t. i, p. 191. 

 Pentaceeos, Gray, 1840. Ann. and Mag. Nat. Hist., vol. vi, p. 276. 



Oreastee, Mailer and Troschel, 1842. System der Asteriden, p. 44. 



Generic Characters. — Form stellate, marginal plates conspicuous, defining the 

 ambitus. Abactinal plates regular, with more or less definite intermediate papular 

 areas. Prominent localised mammillated tubercles or spines present. 



All the fossil species of this genus possess intermarginalia, but do not other- 

 wise approach Sladens' genus Pentaceropsis which possesses this character. Li 

 view of the fact that intermarginalia may occur as a variation in unmistakable 

 recent species of Pentacerus this character cannot invalidate the admission to the 

 present genus of the species about to be described. 



