128 FOSSIL OOLITIC ASTERIAD^E. 



The marginal plates are small, square ossicles, which decrease in size gradually and 

 regularly towards the apex of the rays ; in the specimen figured, which is small, there are 

 from 55 — 60 marginal plates around the border of the most perfect ray, and in larger 

 specimens, where the number of the border plates increase with age, they may amount in 

 a full-grown individual of this species to 80. These marginal plates are very spiniferous ; 

 in addition to the row of thorn-like spines at their distal border, the dorsal plates appear 

 to have been clothed with small spines, from the numerous impressions they have left in 

 the mould, and which are reproduced in the cast. The border is quite straight, and the 

 rays taper gradually and regularly from the base to the apex. 



The ambulacral valleys are wide and well defined ; the small bones bounding these 

 avenues supported one or more rows of short, stout spines, the numerous impressions of 

 which are well preserved in the specimen and have been admirably reproduced in the 

 cast. 



As Prof. Torbes gave no figui'e of Adropeden Orion, nor marked by that name any 

 specimen in the museum in Jermyn Street (then under his care), considerable doubt 

 exists as to the Star-fish he had described as A. OiHon. After the best consideration I have 

 been able to give to the subject, I have come to the conclusion that the fossil I have 

 figured must be the species intended. In the ' Memoirs of the Geological Survey' 

 Prof. Porbes states that all the specimens of A. Orion are from the Oolites of 

 Yorkshire, but in the list of Echinodermata published in Prof. Morris's ' Catalogue of 

 British Possils,' and supplied by Prof. Forbes, this species is said to have been 

 obtained from the Lias of Yorkshire, and the same error is committed regarding A. 

 davcBformis, which is associated with A. Orion in the same formation ; in fact, at the time 

 my esteemed colleague published his notes on British Fossil Asteriadse, the true position 

 of the sandstone containing these moulds of Star-fishes was not known, for by some the 

 rock was called Calcareous Grit and by others Marlstone, whereas, in fact, it is a bed of 

 the Kelloway rock. Astropeden Orion is thus described by Prof. Forbes : 



" A. radiis lineari-lanceolatis, longis, lateribus rectis, angulis intermediis obtusis ; 

 ossiculis marginalihiis omnibus (ossiculis angulorum exceptis) plus-minus ve quadratis 

 spiniferis. 



" Measures eight or more inches in diameter. A very regularly stellate species, 

 having gradually tapering arms, bordered by square plates, which decrease regularly and 

 gradually towards the apices. Each ray is to the diameter of the disc as three and a half 

 to one. There are about forty ossicula on each side of each ray. 



" In the collections of the Marchioness of Hastings, the Marquis of Northampton, and 

 Dr. Bowerbank. All the specimens are from the Oolites of Yorkshire." 



Affinities and differences, — This species resembles Astropeden Phillipsii, Forb., in its 

 general outline and leading characters, but differs from that form in having the marginal 



