DE. GUNTHER OX THE FISHES OF CENTRAL AIMEEICA. 401 



These remarks appear to me to convey very strong testimony in accordance with my 

 own observation on the ichthyological fauna, inasmuch as the author refers the Panama 

 MoUusks generally to the Atlantic fauna. He, indeed, denies the perfect identity of 

 the species, admitting merely an "analogy" between them; but then it is a question 

 whether malacologists do not go too far in making specific distinctions, when they are 

 not even able to express those distinctions " diasrnostically," recognizing the forms 

 merely " by their general habit." Shells are, after all, that portion of a moUusk the 

 formation and development of which is most influenced by the peculiarities (physical 

 and chemical) of the surrounding medium and locality ; and only too many specific 

 forms have been distinguished on account of slight differences in the sculpture and 

 shape of the shells, the importance of which disappears on comparing a large series of 

 examples. However, as I am not prepared to form an opinion with regard to the shells 

 of Central America from my own examination, I am bound to receive the testimony of 

 so celebrated a malacologist as Dr. Morch ; and should his observations prove to be 

 fully correct, they will give an additional interest to this fauna, as proving that the 

 shells of MoUusks suffer change under circumstances in which the specific charactei-s 

 of fishes remain unaltered. 



With regard to fossil shells, Mr. J. C. Moore, who has examined several collections 

 from tertiary beds in San Domingo, has made the observation that " many bear a strong 

 resemblance to shells now living in the Indian Seas and the Pacific, and that one or two 

 appear to be identical" (Quart. Journ. Geol. Soc. 1853, p. 131), and " that a channel 

 or sound may have existed in the equatorial parts during some portion of the tertiary 

 period, by which some few of the tropical shells may have migrated from the one ocean 

 to the other" (ibid. 1850, p. 43). 



Of the other marine animals, the Corals have been made the object of elaborate 

 researches, the various authors arri\dng at somewhat different conclusions. First, 

 Mr. Duncan, in a paper " On the Fossil Corals of the West-Lidian Islands" (Quart. 

 Journ. Geol. Soc. xix. 1863. p. 455), has shown that "in all the calcareous formations 

 which are covalliferous, and are considerably elevated above the level of the Caribbean 

 Sea [being probably of miocenc age], there is a very limited series of Corals witli 

 generic relation to those now existing and characteristic of the West-Indian Coral 

 Fauna, but a predominance of forms resembling those of the present Coral-seas of the 

 Pacific, South Sea, and the Indian Ocean." Tiiis identity of the Corals proves an 

 identical condition of the phj^sical circumstances, and evidently a wide contiiuiity of 

 the West-Indian and Western seas. 



On the other hand, Prof. Veeeill, when speaking of the living Polyi)-fauiKV of the 

 Atlantic and Pacific sides of Central America (Proc. Post. Soc. Nat. Hist. x. 1866, 

 p. 323 et seq.), states that their differences of character are verj- remarkable; that at 

 Panama none of the reef-building corals of Asi)inwall, Florida, or the West Indies 

 occur, nor even any of the genera of the families to which they belong, with the 



VOL. VI. — PART VII. 3 K 



