126 



FOSSIL OOLITIC ASTERIAD^E. 



"A. racUis lanccolatis, longis, acuminatis, ad origines contractis ; angulis intermediis 

 acutis ; ossicidis marginalihus anguloriuii brevibus, in parte latiori radiorum maximis, 

 anguste oblongis, in apicibus radiorum quadratis, 



"This species," lie adds, " measures nearly a foot in diameter. The peculiar form of 

 the rays, which, united by their bases at an acute angle (where the marginal plates are the 

 narrowest), then swell out into a petaloid shape, and again contract into long, linear- 

 lanceolate extremities, distinguishes it from all congeners. Each ray is to the diameter of 

 the disc as three to one. There are about seventy plates on each side of each ray. 



"Marlstone of Yorkshire. It was first described and figured from the Oolites of 

 Germany." 



A comparison of our figure with that of Goldfuss, shows that the German Star-fish 

 although allied to, is specifically distiuct from, our fossil ; the disc is larger in proportion to 

 the body, the area of the rays is likewise greater, and the marginal bones are wider, with 

 a different order of increase ; the intermediate angles are likewise more obtuse ; there is no 

 contraction at the base ; the general form of the ray is entirely different, tapering to an 

 obtuse termination, and having the marginal bones widest at the outer third of the ray ; 

 whereas in Astrojjede/i clanceformis, Wr., the intermediate angles are very acute where 

 the marginal plates are narrowest ; they then suddenly swell out to their maximum 

 breadth, and having attained that width, they gradually and regularly diminish, terminating 

 in fine, Avorm-like extremities. These comparative differences clearly prove that Astro- 

 pecten clavaformis constitutes a well-marked species, entirely distinct from Astropeden 

 arenicolus, Goldf., with which it has hitherto been identified. 



Astropeden davaformis, Wr., is always found in the form of moulds, having the external 

 figure of the body well preserved ; many of these retain tolerably sharp impressions of the 

 different external characters of the species ; from one of these moulds, ray friend, Mr. C. R. 

 Bone, obtained a beautiful cast in gutta percha, showing the general contour of the body ; 

 aided by this and the impressions on the moulds, he has been enabled to produce the very 

 truthful figure of this ancient Star-fish which he has given in Plate XI. 



By the same process we have been enabled to figure, in Plate X a, fig. 3, a remarkable 

 four-rayed variety of this species which I found in the Museum of the Yorkshire Philo- 

 sophical Society. This specimen shows that the Asteriadce of the oolitic fauna were 

 liable to deformities of the same character as are found so frequently to prevail among 

 their congeners of the present day. 



Affinities and differences. — The nearest affinity of Astropeden clavaformis is with 

 Astropecten arenicolus, Gold. ; the most obvious points of difference I have pointed out in 

 the preceding paragraph. It is readily distinguished from Astropeden rectus, McCoy, in 

 which the border of the rays is perfectly straight, without any enlargement near the base. 

 Prof. Forbes described Astropeden Orion as a very regularly stellate species, having 

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



