BRITISH FOSSILS. 



3 



typical species of the genus, and especially with the H. Bailyi 

 of the Gault of Folkstone, from which it is only distinguishable 

 by the absence of any proper fasciole. In H. Bailyi, the peripetal 

 fasciole is narrow and distinct, being more finely granulated 

 than the adjacent surfaces, although a very few tubercles are found 

 encroaching upon it. In H. Murchisonim there is a very wide 

 space surrounding the ambulacral petals, over which tubercles are 

 more thinly scattered ; the miliary granules in this band appear 

 scarcely finer than over the rest of the surface, but this may be 

 partly due to the condition of the specimens, which though silicified 

 are slightly weathered. Ten specimens have been examined. 



Locality and Formation. — At present this species is only known 

 to occur in the Green Sand of Blackdown, Devon, where it is the 

 only urchin of frequent occurrence. 



Description of the Plate. 



Fig. 1. Upper view (of specimen in the British Museum). 



Fig. 2. Under side of same specimen. 



Fig. 3. Terminal Adew (of a more depressed example). 



Fig. 4. Lateral view ; the outline indicates the profile of specimen represented hj 

 figs. 1, 2. This figure (4) is represented as much too depressed, probably 

 from being crushed, the dotted lines represent it more truly. 



Fig. 5. Apical disk magnified. 



Fig. 6. Details of the ambulacra. 



Fig. 7. Anterior ambulacrum magnified. 



Fig 8. Portion of the surface adjoining the right postero-lateral ambulacrum, magnified 



to show the diffused condition of the fasciole. 

 Fig. 9, 10. Tubercles of the lateral surfaces magnified. 



Note on other British species of Hemiaster. 



In addition to the Hemiaster incEguatis, Mr. Morris enumerates the following as species 

 to be described by Prof. Forbes in the Fifth Decade : 



Hemiaster asterias, Gault, Folkstone. 

 H. Bailyi, Gault, Folkstone. 

 H. Morrisii, Chalk Marl, Dover. 



1. Hemiaster asterias, Forbes, Morris's Catal., 2nd edit. 81. 



The specimens with this name attached are not in a svifiiciently well-preserved state 

 to admit of exact comparison and description (the best example being at Edinburgh, 

 and at present inaccessible). The vertex appears to have been more prominent 

 and further back than in the species figured, or in H. Bailyi, and the dorsal ambu- 

 lacra may be longer and narrower in proportion. 



Locality. — Gault, Folkstone. (Mus. Pract. Geology.) 



