Vol. 52.] A DELIMITATION OP THE CENOMANIAN. 165 



specimens from the sands of the Sarthe, many of them would be 

 found to agree with known Cenomanian species. 



The Devon fauna has also a strong affinity with that of the 

 Tourtia of Tournay, in Belgium. Several Tourtia species occur 

 which have not yet been recorded from the Cenomaniari of Western 

 Prance. These are Terebratula arenosa, T. Vemeuilii, Pec-ten 

 Passyi, P. subinierstriatus, Spondylus Omalii, Astarte cyprinoides, 

 A. Koninckii, Avellana Prevosti, and Solarium Thirrianum (?), nine 

 species in all ; besides two species which we have for the first time 

 recognized in the Western Cenomanian, namely, Terebratula capil- 

 lata and T. tornacensis. 



In order to compare this Devon Cenomanian fauna with that of 

 the Warminster Greensand it will be necessary to examine the chief 

 collections of Warminster fossils, not only for the purpose of sub- 

 mitting many of the species to a critical examination,, but in order 

 to weed out of them all the specimens which are preserved in phos- 

 phate of lime, for these have really been obtained from the overlying 

 Chloritic Marl and not from the green sand which lies between it 

 and the Chert Beds. This investigation is not yet completed, but 

 we are able to state that the Warminster Greensand contains 

 comparatively few gasteropoda or cephalopoda, that Ammonites 

 Mantelli and A. navicularis are rare shells in it, and that Turrilites 

 costatus and T. tuberadatus do not occur. 



It is true that many echinodermata, brachiopoda, and lamelli- 

 branchiata are common to the Devon and Warminster deposits, but 

 these are shallow- water forms which would be likely to survive, and 

 to be found in the shallow-water deposits of a slightly later date 

 than that in which they first appear. 



When the fauna found in Devon is compared with that of the 

 Lower Chalk, say that of the Isle of Wight, we find a relationship 

 of just the opposite kind. The Nautili, Scaplrites, Ammonites, and 

 Turrilites which are commonest in Devon are also those which 

 abound in the Chloritic Marl and Chalk Marl of the Isle of Wight. 

 Moreover, there are other species, such as Ammonites Austeni, 

 A. complanatus, A. euomphalus, A. Goupilianus, A. laticlavius y 

 A. leptonema (?), and A. Renevieri, which are much more rarely 

 met with, but which have hitherto been found only in the Chalk 

 Marl or in its basement-bed. When, however, we turn to the 

 echinoderms, brachiopods, and lamellibranchs, we do not find so 

 many of the Devon species in the Chalk Marl as in the Warminster 

 Greensand; but, as no one doubts that the Chalk Marl was formed 

 in a deeper sea than the Warminster Greensand, this absence of 

 certain species is not to be wondered at. 



We would remark that a mere percentage comparison of the 

 faunas of two deposits is not of much value in determining their 

 relative age, even when they occur within the same ancient province, 

 unless there is good reason to suppose that they were formed in water 

 of about the same depth. If, on the other hand, one is a deposit of 

 shallower water than the other, the creatures which are most affected 

 by the difference, such as sponges, polyzoa, brachiopoda, echino- 



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