118 DUDLEY MEMORIAL VOLUME 



Atlantic Coast Pacific Coast 



Lutianus cyanopterus Lutianus novemfasciatus 



Lutianus apodus Lutianus argentiventris 



Lutianus analis Lutianus Colorado 



Lutianus synagris Lutianus guttatus 



Hcemulon album Hcemulon sexfasdatum 



Hcemulon parra Hcemulon scudderi 



Hcemulon schrancki Hcemulon steindachneri 



Anisotremus surinamensis Anisotremus interruptus 



Anisotremus virginicus Anisotremus toeniatus 



Conodon nobilis Conodon serrifer 



Pomadasis crocro Pomadasis branicki 



Calamus macrops Calamus taurinus 



Xystcema cinereum Xystozma simillimum 



Eucinostomus pseudogula Eucinostomus dowi 



Kyphosus incisor Kyphosus analogus 



Isopisthus parvipinnis Isopisthus remifer 



Nebris microps Nebris zestus 



Larimus fasciatus Larimus pacincus 



Odontoscion dentex Odontoscion xanthops 



Corvula sialis Corvula macrops 



Bairdiella verce-crucis Bairdiella armata 



Micropogon furnieri Micropogon ectenes 



Umbrina broussoneti Umbrina xanti 



Menticirrhus littoralis Menticirrhus elongatus 



Eques acuminatus Eques viola 



This list may be greatly extended, but the series noted will illustrate the 

 point in question. Whenever a distinct and sharply denned barrier exists, 

 geminate or twin species may be found on the two sides of it, unless, as some- 

 times happens, the species has failed to maintain itself on one side or the 

 other of the barrier. So far as Panama is concerned, we have evidence 

 that the barrier was raised near the end of Miocene time with no trace of 

 subsequent depression. We can thus form some estimate of the age of 

 separation in at least a small number of closely related species. In this and 

 similar cases it is not possible to conceive of the formation of these species 

 by sudden mutation, or that they would retain their separate existence were 

 the element of segregation removed. While segregation or isolation is not a 

 force, and perhaps not strictly a cause in species formation, it is a factor 

 which apparently can never be absent, if the species retains its independent 

 existence. 



There is no doubt that the distribution of higher animals in general is in 

 accord with "Jordan's law." Examples by the thousand come up from every 

 hand. If we had a hundredth part of the amount of available evidence in 

 support of mutation theories, these theories would pass from the realm of 



