680 REPOKT— 1SC3. 



Tcrdra'vln vifens, Conr., is very probably Wahlheimiu pidri)iafa, Gid. 

 Jinlla ]]etro.'<a, ( our., has the shape of Tornatiiia cnniia, Bd. 

 Ciepiihda j^rorvpia, Conr., is cerX&mly princeps, Midd. 

 Turritella, sp. iiid., resembles Mesalia lactcola. 



'tDoliv7)i petrosmn, Conr., resembles the young of Pn'ene nodosa, Cbemn, 

 luisi's f/enienlt/s, Conr. A similar shell has just been taken at the FaralloTie* 

 by L)r. Cooper. 



121. To correct the general table of " Mollusca of the West Coast of N. 

 America" (First Report, pp. 298-345), and the deductions founded upon it 

 (pp. 34(!-3G7), would involve the necessity of reprinting a considerable por- 

 tion. The student, being now in possession of all the known sources of 

 fresh information, can with his own pen strike out the spurious species, alter 

 the synonyms, insert the newly discovered forms, and make the requisite 

 corrections in the classified results.' 



122. With regard to the tropical fauna, the researches at Cape St. Lucas 

 and in the interior of the Gulf of California, though leaving much to be 

 desired, bear-out the general conclusions arrived-at in paragraphs 78-87. 

 The evidence for the identity of specific forms on the Atlantic and Pacific sides 

 of Central America has been greatly confirmed. Dr. Gould writes, "The 

 doctrine of local limitations meets with so few apparent exceptions that we 

 admit it as an axiom in zoology that species strongly resembling each other, 

 derived from widely diverse localities, especially if a continent intervenes, 

 and if no known or plausible means of communication can be assigned, 

 should be assumed as different until their identity can be proved (vide E. E. 

 MoU. Intr. p. xi). Much studj- of living specimens must be made before 

 the apparent exceptions can be brought under the rule." It has, however, 

 to be borne in mind that the researches of modern geology clearly point to 

 considerable alterations in the existing configuration of continents, and m 

 the consequent direction of ocean- currents, during the ascertained period of 

 many species now living. Nor are we warranted in the belief that the 

 existing fauna in any locality has been created at any one time, or has 

 radiated from any single spot. To study the relations of living shells simply 

 in connexion with the existing map of the world must lead but to partiiil 

 results. The facts accumulating with regard to the British species, by 

 tracing them through the northern drift (now found even on the Snowdonian 

 range), to the oldest crag deposits when Europe was contained in far different 

 boundaries, show how altered may have been the configiiration of the new 

 world when the oldest of its molluscs were first created. Coordinately with 

 the glacial period. Central America may have been a group of islands ; co- 

 ordinately with the creation oi Saxicava pho2adis and fJhrysodomus antiqims, 

 the gulf-weed may have floated between the Eocky Mountains in the 

 archipelago of West America, and Japanese molluscs may have known how 

 to migrate to the Mediterranean shores. Dr. Gould's position may there- 

 fore be accepted in theory ; yet, in practice, the " imperfection of the geological 

 record"*, and even of our knowledge of existing species and their variations, 

 demands that the greatest caution be exercised in building results on deduc- 

 tions from our ignorance. Already the fossil Malea lingens of the Atlantic 

 has proved a " Eosetta Stone " to interpret the Cyprcpa exanthema , Purpura 

 jiatida, and other Caribbean shells of the Pacific ; and as the geology of the 

 West Coast advances, so may Ave expect to find traces of previous denizens of 



* No student of geographical distribution should omit to weigh carefully the chapter 

 on this subject in Darwin's ' Origin of ISpecies,' and the information given in Lj'ell's 

 ' Antiquity of Man.' 



166 



