ANIMAL NATURE OF DIATOME^!. 393 



as belonging to Gallionetta or Melosira, and I propose 

 to name it Melosira (Pleurosira) Baileyi. 



The celebrated Kiitzing, to whom I communicated 

 these remarks, replies, " your Melosira (Pleurosira) ther- 

 malis is in no respect different from the Odontella poly- 

 morpha. I have compared your specimen with that of 

 Montague. There are even found the delicate (zarteri) 

 points upon the shield, as in the other which I have 

 inadvertently omitted in my figure. Your specimen is 

 certainly an Odontella, although the articulations are 

 cylindrical (teretes), for it is the same also in the 0. aurita. 

 I think of uniting, in future, the Biddulphiea3 with the 

 Tripodiscieae." 



Although I have had an opportunity of examining 

 fragments only of Montague's Istlimea polymorplia, ad- 

 hering to an imperfect specimen of Polysiphonia subti- 

 lissima from Cayenne, with which the celebrated author 

 favoured me, I am still positive in treating the matter 

 differently. It is admirably figured by Kiitzing; the 

 articulations are not cylindrical, and though obtuse and 

 slightly prominent, the lateral processes are very evident. 

 Whether this belongs to the same genus as other Odon- 

 tellce, and whether that genus belongs to the family of 

 Biddulphiese, and to the order Areolatse, is a question to 

 which we shall return. 



Now, resuming all that has reference to the family of 

 Melosirese, we shall find, as a character common to them 

 all, the circular figure of the vertical section parallel to 

 the lateral surfaces ; a character which, as well as the 

 other, of a radiated disposition of the striae upon the 

 lateral surfaces, we shall find repeated in the family of 

 Coscinodisceas, which, having the shield of a cellular struc- 

 ture, belong to the tribe of Areolatae. Perhaps we may 

 suspect some Melosira (sulcata, decussata, lirata,} to be 

 furnished with the same organic condition, and hence 

 arises a fresh doubt respecting the systematic value that 

 has been ascribed to it. 



In general we may also say, that in the Melosireae the 



