92 



Guide to the Invertehrata. 



Echi- Carboniferous Limestone from Bristol (No. 75,724) shows that the 



noidea. gpi^es were often of great length. 



^^vm^^ In tlie Jurassic system the Echinoidea become of great geological 

 Wall-cases importance. The collection (Table-cases 76 and 77) includes 

 16-17, most of the specimens figured by Wright in his monograph 

 of the Oolitic Echinoderms, published by the Paleeootographical 

 Society. The successive faunas are of great interest, beginning 

 with comparatively simple forms, such as the Cidaris Edwardd^ 

 Acrosalenia minuta, and Diademopsis Bowerhanhi, from the Lias. 

 With the exception of the Cidaris, the species from this horizon 

 are small, and apparently grew under somewhat unfavourable 

 conditions. In the Lower Oolites, however, limestones become 

 abundant, and the seas were more suited to sea-urchins. Many 



Table 

 cases 

 76-78. 



Fio. lid.— ralf^cchinuseUipticus, M'Coy. Carboniferous Limestone : Ireland. 



a, side-view of the entire test. 



b, portion of one of the ambulacral areas, enlarged. 



c, a single hexagonal interambulacral plate. 



new types therefore appear, and are represented by massive 

 forms. The most characteristic genera in the Inferior Oolite 

 are Clypeus, Pygaster, Ilolectypm, and Stomechinus. The most 

 interesting genera are probably Hyhoclypeus, Galeropygus, and 

 Collyrites. The succeeding fauna in the upper part of the 

 Lower Oolites has new species of some of these genera, while 

 Acrosalenia and Uemicidaris (Fig. 150) become abundant. Some 

 fine slabs of these are shown in Table-case 77, while still larger 

 Wall-cates ^P^^""^'^^8 are shown in Wall- cases 17a and 15b and c. In the 

 17a, 16b, 0. Corallian the species are fewer, but of great interest. Cidaris 

 is represented by two fine species — C. Blumenhachi and C. flori- 

 gemma. The largest known Hemipedina is exhibited in Table- 

 case 77, and close beside it is the prettily ornamented Glypticus 



Table 

 case 77, 



