360 PKOCEEDIITQS OF THE GEOLOGICAL SOCIETY. [March 8, 



died out in it, and that the coral-fauna of the period nearly equals 

 that of the Midtertiaiy age. Yet during this vast lapse of time many 

 species of Cephalopoda, Mollusca, and Echinodermata were living 

 out of their former zone, were competing with the dwellers of the 

 sea into which they emigrated, and finally returned to their original 

 position. There was abundance of time for any amount of diffusion ; 

 and doubtless the strong species varied, as is their wont, and left 

 their remains over vast areas. Now the Echinodermata and some of 

 the other fossil remains from Bagh and South-eastern Arabia are 

 represented in the faunse of all the divisions of the European Chalk 

 between the Gault and the Chalk- with -flints. They may have origi- 

 nated in the Asiatic Chalk, and may have emigrated to the districts 

 referred to in Europe ; the reverse may have happened ; or, as is 

 more probable, the species arose in various districts by variation from 

 species competing strongly, perhaps under changes of physical con- 

 ditions, and the Bagh and South-eastern Arabian beds may represent 

 only one or all the European series between the Gault and Upper 

 Chalk. 



9. Remarhs on the Identity, Persistence, and Vmnability of the 

 Species. — It has been mentioned that the European Upper Greensand 

 and its associated strata are represented in the equivalent deposits at 

 Bagh and in South-eastern Arabia by identical species, varieties of 

 species, and by a representative species. The common Cretaceous 

 facies of the faunse is thus retained, although there are forms in 

 them which refer both to earlier and later ages. Thus the variety 

 of Echinohrissus suhquadratus, which is a Neocomian species, is a 

 common fossil at Bagh, and its specimens are numerous in the small 

 collection. 



DiiFering from the type in having a very slight instead of a decided 

 incurvation posteriorly, the variety presents all the other specific 

 attributes, and it occupies the same relative position in the Bagh 

 fauna which varieties of certain Midtertiary s]3ecies do in the exist- 

 ing distribution of living beings. The Hemiasters, on the contrary, 

 connect the Middle with the Upper Cretaceous, and with the Tertiary 

 Echinodermata. The new Cottaldia is representative of the Cottal- 

 dia Beneitice, Koenig, sp., so characteristic of the Tourtia ; and it is 

 reasonable to infer, from the great similarity of their structure, an 

 adaptation to the same mode of life. The new species clearly fills 

 up the vacancy produced by the absence of the well-known form, 

 which would cause a sensible gap in any series of Upper Greensand 

 Echinoderms. 



There appears to be an indisposition on the part of some distin- 

 guished geologists and naturahsts to admit the occurrence of the same 

 species in distant strata or in remote areas. The slow progression of 

 species, and their constant competition with others diu'ing their dif- 

 fusion, have suggested that greater or less variation must occur, and 

 that the original type is never found in very remote localities, but 

 varieties of it, some of which are sufiiciently permanent to be con- 

 sidered closely allied species. Some naturalists assert that even if 

 the distant forms be identical to the eye they must be specifically 



