428 DAVIDSON ON FOSSIL BRACHIOPODA. CHAP. xxn. 



as Leptcena depressa, which we must now call, in obedience to 

 the law of priority of nomenclature, Anomites (or Stropho- 

 mena) rhomboidalis, Wahlenberg. No less than fifteen com 

 monly received species are demonstrated by Mr. Davidson, by 

 the aid of a long series of transitional forms, to appertain to 

 this one type, and it is acknowledged by some of the best 

 writers that they were induced to give distinct names to some 

 of the varieties now suppressed on purely theoretical grounds, 

 namely, because they found them in rocks so widely remote 

 in time, that they deemed it contrary to analogy to suppose 

 that the same species could have endured so long a mode of 

 reasoning analogous to that which leads some zoologists and 

 botanists to distinguish by specific names slight varieties of 

 living plants and animals met with in very remote countries, 

 as in Europe and Australia, for example, it being assumed 

 that each species has had a single birth-place or area of 

 creation, and that they could not by migration have gone 

 from the northern to the southern hemisphere across the 

 intervening tropics. 



Examples are also given by Mr. Davidson of species which 

 pass from the Devonian into the Carboniferous, and from that 

 again into the Permian rocks. The vast longevity of such 

 specific forms has not been generally recognised in conse 

 quence of the change of names, which they have undergone 

 when derived from such distant formations, as when Atrypa 

 unguicularis assumes, when derived from a carboniferous 

 rock, the name of Spirifer Urii, besides several other syno 

 nyms, and then, when it reaches the Permian period, takes the 

 name of Spirifer Glannyana, (King) ; all of which forms the 

 author of the monograph, now under consideration, asserts to 

 be one and the same. 



No geologist will deny that the distance of time which 

 separates some of the eras above alluded to, or the dates of 

 the earliest and latest appearances of some of the fossils 



