262 A. &; R. Bell— On the English Crags. 



the Crags. Both the upper and lower Crag deep-sea fauna have 

 more species in common than have the deposits formed in shallower 

 waters, such as Walton-on-the-Naze and Butley Corner. Yet, in 

 comparing collections, even from these deeper sea-bottoms, we find 

 sufficient evidence of change, either in the size, or relative abundance 

 of forms, or presence of particular species, and the absence of others. 



The aspect of both the shallow zones of Walton-on-the-Naze and 

 Butley differs very materially, one looking as if of southern origin, 

 the other of northern ; this, of course, is effected by the outgoing 

 and incoming of characteristic forms. The greatest variation is, 

 perhaps, that presented by the Echinodermata, five or six Echini 

 being peculiar to one deposit, and one to the other. 



Having thus briefly indicated the areas over which our proposed 

 division extends, we pass on to the evidence upon which such divi- 

 sion is founded, and to this end we give, first, an abstract of the 

 species of MoUusca contained in each division, and of those which 

 they have in common. 



In the Lower (or Coralline) Crag 382 species. 



„ Middle (or older Eed) „ 324 „ 



„ Upper (or newer Redj „ 196 „ 



„ „ (Fluvio-marine) „ 163 „ 



Common to both divisions of the Eed Crag... 217 „ 



Peculiar to the Lower Crag 170 „ 



„ „ Middle „ 129 „ 



„ „ Upper (marine) 33 „ 



Or including the fluvio-marine species €0 „ 



Total number of species in the Eed Crag, i.e. Middle and Upper (marine) 

 Crags, 407. 



Beyond these tables we do not think it necessary to go at present, 

 and shall therefore notice only a few of the more prominent cha- 

 racters of each division. 



Only one species of extinct Helix has been found in the Eed 

 Crag; it was obtained at Walton and Waldringfield, All the 

 land-shells of the upper horizon are of recent British forms. We 

 would call attention to the occurrence of Paludina parilis and of 

 Corhicula fluminalis at Waldringfield as being a step backwards in 

 time of the known occurrence of these two freshwater species. 



Of the Brachiopoda little, can be said, one of the only two species, 

 i.e. Terebratula grandis, var., occurring in both series. In one respect 

 this is interesting, as we have been able to trace the shell from the 

 fry to the adult state, with the perfect loop, and this form or variety 

 is one which Mr. Davidson informs us is not found in the Coralline 

 Crag. The circular ridges are stronger, the foramen largei", even in 

 young specimens, and the neck or beak much longer, and more 

 constricted than is the case with the specific type. Bhynchonella 

 is confined to one horizon at present. 



The Lamellibranchiata of the Lower division, when compared 

 with those of the Upper, have an older facies, and one that indi- 

 cates a warmer climate than prevailed afterwards. Perhaps this 

 may be better understood by our mentioning some of the peculiar 

 shells, thus Ostrea cochlear, Pecten septemradiatus, Lima inflala, 



