Nov., 1861, p. 336.) This observation, with the discovery of the 

 inner plate of the Coscinodiscus, and its structure, makes the analogy 

 of the structure of the two genera complete, and may be con- 

 sidered as proving the existence of the inner plate in this genus. 



Another point in the structure of the valve has been a subject of 

 much difference of opinion — some contend that the areola are ele- 

 vations, others that they are depressions. Dr. J. W. Griffiths gives, 

 in the Micrographical Dictionary, his reasons for considering them to 

 be depressions. I have reasons for thinking that neither party has 

 the true explanation of the structure. My opinion is that the exte- 

 rior of the shell is smooth or nearly so, and that the borders of the 

 hexagons, or other shaped areolae, and cost^e of the costate forms, are 

 internal projections from the outer plate, as on the under side of the 

 leaf of the Victoria Regia, intended to give strength to the cell with 

 the smallest quantity of material. This will explain the trace of the 

 hexagons seen on the inner plate of Heliopelta, as only the projecting 

 wall of the areolas would come in contact with the inner plate. Dr. 

 Griffiths reasoned that the areolae were depressions because they were 

 the thinnest parts of the shell ; the facts are correct, but the inference 

 may not be, as there is another explanation of the phenomena. 



In company with Dr. C. T. Jackson, I have dissolved a shell of Cos- 

 cinodiscus under the microscope, with caustic potash, and found that 

 the area of the cellules was dissolved before the walls, and that there- 

 fore they are the thinnest parts, as Dr. Griffiths judged from the opti- 

 cal effect. 



Mr. Marcou stated that the last steamer for Europe from 

 this port had taken out clams, oysters, lobsters, and other 

 marine animals of our coast, for the purpose of acclimatizing 

 them on the Atlantic and Mediterranean coast of France. 



A donation of insects, fish, crustaceans, a snake, and a 

 specimen of the wild potato, from the island of St. Lorenzo, 

 on the coast of Peru, opposite Callao, was presented in the 

 name of Dr. C. F. Winslow. A letter accompanied the 

 specimens, from which the following are extracts: — 



The potato is the most important, which I send with the hope 

 that some of you will cultivate it. It is the wild potato, and the 

 same as those which were found by the early Spanish settlers in this 

 country, and first taken from St. Lorenzo for cultivation, and from 

 which have probably sprung all the varieties of potatoes cultivated 

 by civilized nations. Its favorite haunt seemed to be in light, 

 fine soil, near or under the edge of stones. It is not very abun- 

 dant on that part of the island which I explored. Helices abound 



