DR. GUNTHER ON THE FISHES OF CENTRAL AMERICA. 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 
Mollusks 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 “diagnostically,” recognizing the forms 
merely ‘“‘ by their general habit.” Shells are, after all, that portion of a mollusk 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. Mérch; and should his observations prove to be 
fully correct, they will give an additional interest to this fauna, as proving that the 
shells of Mollusks suffer change under circumstances in which the specific characters 
of fishes remain unaltered. 
With regard to fossil shells, Mr. J. C. Moorr, who has examined several. collections 
from tertiary beds in San Domingo, has made the observation that ‘‘ many bear a strong 
resemblance to shells now livmg 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 Cora/s have been made the object of elaborate 
researches, the various authors arriving at somewhat different conclusions. First, 
Mr. Duncan, in a paper “On the Fossil Corals of the West-Indian Islands” (Quart. 
Journ. Geol. Soc. xix. 1865, p. 455), has shown that “in all the calcareous formations 
which are coralliferous, and are considerably elevated above the level of the Caribbean 
Sea [being probably of miocene age], there is a very limited series of Corals with 
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.” This identity of the Corals proves an 
identical condition of the physical circumstances, and evidently a wide continuity of 
the West-Indian and Western seas. 
On the other hand, Prof. Verrit, when speaking of the living Polyp-faune of the 
Atlantic and Pacific sides of Central America (Proc. Bost. Soc. Nat. Hist. x. 1866, 
p- 323 et seq.), states that their differences of character are very remarkable; that at 
Panama none of the reef-building corals of Aspinwall, 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. 3K 
