On the Temperatnre of the Sea, ^c. 295 



has ever been found in Europe, it is going too far to consider that as 

 a proof of the identity of the beds in which it occurs with our green 

 sand. The smooth varieties of it, which are said to resemble the G. 

 hahotoidea of Min. Conch, we have not seen ; but it probably is that 

 species : if so, the consideration of it with Gryphcea convexa of Mr. 

 Vanuxem and Dr. Morton, (which is G. globosa of Min. Conch, and 

 Podopsis gryphaeoides of the French, and occurs in green sand, as 

 well as chalk) Baculites and other shells, will go far to prove what 

 those gentlemen have suggested, that the beds in which these shells 

 occur are the equivalents of the green sand and chalk formation of 

 Europe." 



1 will here observe, that although some of the Exogyrse of New 

 Jersey are ribbed, and others are not, I believe them to be one and 

 the same species, inasmuch as the young shells are mostly smooth, 

 and specimens are found with every variety of surface, from incipient 

 ridges to elevated costse. Another fact, noticed by Mr. Say, is, that 

 in old shells the ribs often became indistinct, and even obsolete. It 

 seems therefore impossible to derive specific distinctions, in this in- 

 stance, from the costce of the Exogyrse ; and we must be content to 

 consider all our American specimens as identical until we can discov- 

 er some less variable characters by which to distinguish them. 



Although the Exogyra costata and E. haliotoidea appear to be 

 analogues, they are evidently distinct species ; which remark I am 

 disposed also to apply to the EngHsh Gryphaea globosa, and the 

 American G. convexa. 



[The subject will be resumed in the next number of the Journal, 

 and will there be illustrated with plates. — Editor.'] 



Art. IV. — Fragment from Per on, with notices from other voyagers, 

 , on the Temperature of the Sea, at great depths, far from Land. 



Mr. Silliman — The following is translated from the " Voyage de 

 Decouvertes Aux Terres Australes," section 4. Vol. II. p. 334. It 

 seems to me that the /ac^s detailed by M. Peron are inconsistent with 

 the theory of M. Cordier, as to central heat, if the}^ do not prove 

 conclusively its entire fallacy. The thermometer used by Peron 

 was Reaumur's, it will be easy to estimate the changes of tempera- 

 ture by Fahrenheit, if it is recollected that the zero of Reaumur is 

 the freezing point or 32° of Fahrenheit, and that four degi-ees of the 

 former are equal to nine of the latter. Yours, 



Steuboiiville, Ohio, Sept. 20tli, 1829. ' BeNJ. TapPAN, 



