258 On tJie Fossil Concliology of Minchinhampton, 



of the Fimbria bed ; lastly, in the upper beds of the Great Oolite it 

 is again abundant and of its standard bulk. 



Next as to the gregarious habit3 of certain species : — Bussage, 

 a small hamlet north of the vale of Brimscomb, produces in its 

 shelly Great Oolite a large assemblage of an undescribed species of 

 Terebratula somewhat resembling T globata,hut very rarely having 

 both valves in juxtaposition, and seldom found in any other locality. 

 In the limestone beds of the upper fossiliferous series, one locality 

 has produced a dense assemblage of a fine bivalve which seems 

 to belong to the new genus Cardilla of Deshayes, although ge- 

 nerally in these beds it is rare. The compact structure of the 

 rock renders it nearly impossible to disengage them in a perfect 

 state, but the fine striae of the shell are well preserved, and the 

 character of the species evident ; its sudden advance in size when 

 compared with the small fossil shell upon which the genus was 

 founded is remarkable, and justifies the specific appellation of 

 grandis. 



The association of species at the locality in question is curious : 

 the whiteness of the Cardilla limestone displays every testaceous 

 fragment in strong relief, and enables us to discover that the 

 Cardilla is the only bivalve, and that it is accompanied by a 

 Purpuroidea, and more sparingly by three large Notices, all of 

 which probably constituted checks upon its superabundance. 

 Monotis radiata occurs by myriads immediately beneath the 

 planking beds on Minchinhampton Common, and the gregarious 

 habits of Perna mytiloides may often be shown in a small hand 

 specimen of rock. Cardium Beaumonti, Archiac, is found only 

 in the upper beds, where, in abundance, they rival the Perna my- 

 tiloides of the lower series. In spots where the rock becomes a 

 barren sandstone far away from all detritus of shells, and pro- 

 bably deposited at greater depths, a cluster of Pholadomya con- 

 csntrica or P. Murchisonice sometimes appears ; nor are any shells 

 of the genus Pholadomya ever found in the shelly beds of the Great 

 Oolite ; they are likewise absent in the Fimbria bed of the Infe- 

 rior Oolite, and it may be safely predicted, that they never will 

 be found in the shelly roe-stone of the vicinity of Cheltenham ; 

 these beds were evidently deposited in a shallow sea, and por- 

 tions of them even possess a littoral character. The little know- 

 ledge we possess of the habits of the recent Pholadomya Candida 

 is in exact accordance with this fact. At one locality the upper 

 beds have produced a dense colony of Terebratula media to the 

 exclusion of all other shells. Lucina lyrata, Pholadomya truncata, 

 P. nana, Ceromya excentrica and Ceromya semistriata are like- 

 wise never found isolated. 



The changes of external characters produced by growth alone 



