ON THE ECHINOIDEA. 



461 



Section of ihc Urchin Quarry near Cirencester. 



No. 1. 



2. 



3. 



4. 



Bradford Clay kepuesentative, 

 with Terelratula digonn, Sow. 



Great Oolite. 



Marly Vein, with Acrosalenia pnstic/ata, 



Forb. 



Band of Stone. 



Clay Bed, 



Great Oolite. 



Si.K feet. 



Six feet. 



Two inches. 

 Four inches. 



Two feet. 



" The bed No. 3 is the one where the urchins Acrosalenia pusiulata, Forbes, 

 occur. The only other specimen of a different kind is Holeciypiis depresses, Lamk. 

 The beds Nos. 2, 3, 4, and 5 have been called Forest Marble, which we do not approve 

 of, as bed No. 2 is as decidedly freestone as the bed No. 6." 



Thomas C. Brown, Esq., of Cirencester, has likewise kindly furnished me with the 

 following note on this remarkable urchin-bed. He says — " In January, 1859, a great 

 number of the Acrosalenia ^usiulata were fouwd at Cirencester in the Great Oolite, eight or 

 ten feet below the top of that stratum. A space of four or five yards square, two inches thick, 

 was filled with this urchin, about 1000 in every superficial yard. They were found one 

 upon another, about three deep, in a bed of white, marly clay. The tests were filled with 

 this clay, and were found in a high state of preservation, with their spines recumbent upon 

 them. It is presumed that this species is gregarious, and that a shoal of them were 

 choked in a stream of mud ; that they fell down together Avith the mud upon the 

 Oolitic Rock then in course of formation, and were covered up with subsequent deposits of 

 Oolitic matter. This species is not numerous in this district. The tests vary in size and 

 shape, probably from a difference in age and sex, and there is great diversity in the form 

 and number of the plates forming the apical disc. After repeated washings of the clay in 

 water, fragments of the test were found, with broken spines of the larger and smaller ones ; 

 some of the latter are of a purple colour, many loose teeth, and one perfect set, together 

 Avith Oolitic grains, but scarcely any other fossil." 



