48 FQURTH REPORT 1834. 



European seas. I have accordingly procured from my friend 

 Mr. Conrad a catalogue of the known marine shells inhabiting 

 our coast from Louisiana to Maine. This I should have been 

 glad to insert, as such a list has not before been made, but 

 for the length to which this Report has grown under my hands. 

 It is important to know, however, that the whole number of 

 marine species, excluding those of the West Indies and the 

 southern region of the Gulf of Mexico, does not much exceed 

 200. It is possible that by dredging our coast a large accession 

 to the list might accrue, yet it is apparent that the North Ame- 

 rican border of the Atlantic is not prolific in Testacea ; and the 

 same seems to have been equally the fact during the several 

 tertiary periods. 



Mr. Conrad and Dr. Morton have arranged with care the fol- 

 lowing viseful table of recent species common to the European 

 and American coasts of the Atlantic. 



1. Purpura Lapillus. 17. Thracia convexa. 



2. Buccinum undatum. 18. Solecurtus fragilis. 



3. Natica canrena. 1!). Glycimeris siliqiia. 



4. Fusus islandicus. 20. Cardium islandicum. 



5. Cyprina islandica. 21. groenlandicum. 



6. Saxicava rugosa. 22. Tellina punicea. 



7. Lucina divaricata. 23. Venus niercenaria. 



8. Pholas cvispata. 24. Pecten islandicus. 

 9. costata. 25. Strigilla carnaria. 



10. Anomia Ephippium. 26. Balanus ovularis. 



11. Solen ensis. 27. elongatus. 



12. Mya arenaria. 28. Anatifera dentata. 



13. Mytilus edulis. 29. vitrea. 



14. Modiola papuana. 30. laevis. 



15. Mactra deaurata. 31. Teredo navalis. 



16. Spirorbis nautiloides. 32. Serpula . 



The above list is likely to be sensibly augmented as fresh 

 species are discovered. 



Here are 32 species in 200 (or one sixth) common to the two 

 sides of the Atlantic, while, as we have seen, in 195 fossils of 

 our middle tertiary there are but 6 ; and in 210 eocene fossils 

 also only 6 which inhabited both continents during those re- 

 moter {eras. We shall presently see, that during a still earlier 

 period, that of the secondary cretaceous group, there was but a 

 single species in 102 described which had this wide dispersion 

 over both continents. Whether we shall discover a like dis- 

 similarity in the organic remains of yet older formations is a 

 question still to be solved, and it will require much preliminary 

 labour and research. 



In concluding this survey of our tertiary formations, I ought 



