130 



FOSSIL OOLITIC ASTERIADiE. 



Description — This species is characterised by its long, linear, narrow, straight-sided 

 rays, bordered by two rows of large marginal, quadrate ossicula, much lengthened trans- 

 versely, each bone being about one third the length of the diameter of a ray ; the whole of 

 their convex upper surface is covered with small tubercles, as shown in our figure ; at the 

 posterior side of each bone is a row of three or four larger tubercles, which supported large 

 spines ; there are about ninety marginal bones around the border of a ray ; along the 

 inner side of the marginal plates a series of smaller quadrate ossicles is placed, three of 

 these equalHng the length of two of the marginal bones ; the ambulacral ossicula are like- 

 wise covered with minute tubercles, and on the centre of each bone is one large tubercle 

 for supporting a gigantic spine. 



This Star-iish is for the most part known to us by horizontal sections of the skeleton 

 as figured in PI. XII. In one instance only have I seen the marginal bones free from the 

 matrix, and these are figured in the same plate ; this specimen which formerly belonged 

 to the collection of Mr. Bean, of Scarborough, is now contained in the York Museum. 



The diameter of the disc to that of the body is as two to nine, and many specimens 

 attain a foot in diameter. The hard crystalline character of tlie Calcareous Grit in which 

 this fossil is found conceals all details of the external structure of the ossicula beyond those 

 I have figured. 



Jfflnities and differences. — This species is well characterised by the narrowness and 

 straightness of the rays and the large size of the marginal plates. It differs, therefore, from 

 Astropecten clavcpformis in the absence of the enlargement at the inner third of the rays 

 which constitutes so remarkable a character of that form. Count Miinster, in his 

 ' Beitrage zur Petrefacten-Kunde^ figured in pi. xi, fig. 1, of that work, a Star-fish under 

 the name Asterias Mandelsloki obtained from the sandstone of the Inferior Oolite near 

 Aalen, which has some resemblance to Astropecten rectus, but the marginal plates are 

 proportionately narrower, and the ambulacral furrows considerably wider in the Aalen 

 fossil than in our species. 



Locality/ and Stratigrapldcal Position. — This species is obtained by splitting open the 

 large nodules which fall out of the Calcareous Grit under Piley cliffs, near Piley Brig, on 

 the Yorkshire coast. Mr. Peter Cullen informed me that all his specimens were obtained 

 from this locality ; they are, however, merely horizontal sections of the body and arms, for 

 in only one specimen have I seen the form and surface of the marginal plates, I obtained a 

 very large specimen of this species from the Calcareous Grit near Calne, in Wiltshire, 

 which measures from the centre of the disc to the end of the ray six inches, giving the 

 dimension of one foot to the body. 



