402 Unionid(B of the Country of the Iguanodon. 



Art. XVII. — Oil the Unioriidce of the River of the Country of the 

 Iguanodon; by Gideon Algernon Mantell, M.D. F.R.S. &c. 



Clapham Common, England, Aug. 24, 1844. 



TO PROFESSOR SILLIMAN. 



My dear Friend — Although but a few weeks have elapsed 

 since the publication of " The Medals of Creation," in which it 

 is remarked, that " in number, variety, and beauty, the Unionidae 

 which inhabit the rivers of North America, present a striking 

 contrast with the few and homely British fresh-water muscles ; 

 and that in a fossil state there are no shells of this family at all 

 comparable with those of the United States," I have great pleas- 

 ure in acquainting you that the above observations may now be 

 modified, for I have discovered in the Wealden strata of the Isle 

 of Wight a species of Unio as large and massive as are the splen- 

 did shells of the Ohio and the Mississippi. 



You will probably remember that when you so liberally sup- 

 plied me many years since with a fine series of the recent spe- 

 cies, that I expressed a hope of sooner or later proving that the 

 lakes and rivers of the country of the Iguanodon were tenanted 

 by Mollusca as gigantic as those of America ; that wish is now 

 realized. You are aware that several small species of Unio oc- 

 cur in considerable numbers in the sandstones and limestones of 

 Tilgate Forest, and also enter into the composition of some of 

 the varieties of Sussex marble ; but the largest ^ecies hitherto 

 described (the Unio Mantellii of Dr. Fitton) does not exceed 

 two inches in length by one in altitude. During a brief sojourn 

 in the Isle of Wight a few weeks since, I re-examined the Weal- 

 den deposits which emerge from beneath the lower arenaceous 

 strata of the chalk, along the southern shore of the island, and 

 extend from near Fresh-water Gate towards Atherfield ; a line 

 of cliffs peculiarly interesting to me, from the fine section ex- 

 posed of the laminated sandstones and shales of the Wealden ; 

 and which in that locality abound in the fossil remains of rep- 

 tiles, mollusca, and plants, peculiar to that formation. On my 

 late visit innumerable fragments of fossil wood were exposed 

 along the strand, having been washed out of the fallen masses of 

 strata by the waves, which at high tides dash against and under- 

 mine the base of the cliffs. At low water numerous trunks of 



