BRITISH FOSSILS. 



lateral interambulacral segments, and 10 above the vent in the 

 posterior segment. The infra-anal portion of the latter is composed 

 of two series of five irregularly polygonal plates each ; they are 

 remarkable for presenting gibbosities at regular intervals. In the 

 inferior portions of each postero-lateral ambulacrum there are 

 7 plates in each series. These are polygonal, large, and elongated, 

 and bear the pairs of pores, which are minute and oblique, close to 

 their inner angles. The pores of the ambulacra around the mouth 

 form an obscure star. 



The fasciole passes beneath the anus with a curve, and runs 

 along the sides just above the margin, but becomes obscure or lost 

 upon the anterior interambulacral segments. It is narrow, and free 

 from intermingled tubercles. On bad specimens it can hardly be 

 traced, but upon good ones is very evident. 



The apical disk is covered with granules similar to those of the 

 neighbouring plates, so that its elements are but obscurely defined ; 

 it is composed of four perforated genital and five perforated ocular 

 plates. An imperforate genital plate is also present, but insigni- 

 ficant. The madreporiform body is very indistinctly marked. The 

 two postero-lateral genital plates are long, and cause a considerable 

 separation of the summits of the two hinder ambulacra from the 

 other three. In flint casts there are strong indications of the 

 presence of a sand tube like that in Ananchytes ovata. 



Gardiaster granulosus grows to a considerable size. Moderately 

 large and evidently adult specimens in the Museum of Practical 

 Geology, to which they were presented by Mr. S. P. Woodward, 

 measm-e 2 inches and ^^^^ in length, the same in breadth, and 

 1 inch ^-^ th in height. Other examples have a greater height in 

 proportion to the breadth, or a greater length in proportion to the 

 width. 



Locality and Geological Position. First observed as British by 

 Mr. Samuel Woodward, who recorded it {Spatangus cordiformis) 

 as rare in the Upper Chalk at Harford Bridge, and as common in 

 the "Medial Chalk'' at Swafi'ham and Thetford, all Norwich loca- 

 lities. The Holaster cequalis of Colonel Portlock has been already 

 noticed as identical with it (the original specimens have been com- 

 pared), and was found in the Chalk of Londonderry. 



Explanation of the Plate. 



Figs. 1. 2. 3. and 4. Different views of a Norwich specimen of Cardiaster granulosus. 

 Fig. 5. A flint cast ; one of the original specimens of Holaster equalis of Portlock. 

 rig. 6. Ambulacral and inter-ambulacral plates from the centre of the sides. 



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