depth, Avbere the temperature was only three-tenths of a 

 degree centigrade (nearly the freezing point), were found 

 living polyps, mussels, tunicata, annelides, and bright-colored 

 crustaceans. The same naturalist had found ammonites 

 (probably Jurassic), and loaves resembling those of the pal- 

 metto (probably miocene), at Spitzbergen. 



Ml'. Stodder read a paper " On the structure of the Valve 

 of the Diatomacere," and exhibited siDCcimens of great beauty 

 imder the microscope. 



On the Structure of the valve or the Diatomace^. By 

 Charles Stodder. 



There are recorded a few observations which mention the exist- 

 ence of more than one plate of silex in the valve of some three or 

 four species of Diatoms. Mr. Shadbolt (Trans. Mic. Soc. 1st series, 

 vol. iii., p. 49) describes the valve of Arachnoidiscus Japonicus as 

 consisting of two layers. Mr. Ralfs (Pritchard's Infusoria, 4th ed., 

 p. 839) says the valves of Aclinoptychus undidatus " frequently con- 

 sist of two dissimilar plates, one having the usual character, the other 

 being triradiate and minutely punctate, and which has been described 

 as a new species by Mr. Eoper, who first observed it detached from the 

 true valve. He and others have since found the plates in situ." Dr. 

 F. W. Lewis (Notes on new and rarer species of Diatomaceas, Phil., 

 1861, p. 6), describing Naiiicida marginata^ speaks of "the outer 

 silicious plate." Schleiden (Pritchard, 4th ed.,p.41) speaks of "two 

 leaves lying one over the other." Mr. Brightwell says of the lorica of 

 Triceratium that " the valves are resolvable into several distinct lay- 

 ers of silex, dividing like the thin layers of talc." (Pritchard, p. 49.) 

 These are all the authorities I can find that intimate the existence 

 of more than one plate of silex in the valve. 



Ehrenberg describes several species of Diatoms as " veiled," — a 

 most happy term as expressive of the appearance of those species to 

 which it is appHed. Neither Ehrenberg nor any other microscopist 

 has offered any explanation of the cause of this appearance. Among 

 the species thus distinguished, are the four species of Heliopelta, 

 though the fact is not mentioned in any of the pubHshed descrip- 

 tions, all of which are more or less imperfect. 



Some time ago I found a broken specimen of Hellopelfa, which 

 exhibited clearly portions of the valve with the normal characters of 

 the genus, and, extending beyond the brok'en edges, portions of 

 another and inner plate of an entirely different structure. A few 

 months since, Mr. J. S. Melvin gave me specimens of a Diatom, as 

 possibly a new species. On examination of these I found that he 



