98 /Sketch of the Infusoria of the family Bacillaria, 



3. Navicula . (Pi. 2, fig. 18.) This figure represents a pan- 



duriform species, very much contracted in the middle. It occurs in 

 peat from a salt marsh near Stonington, Conn. 



4. Navicula . (PI. 2, fig. 19.) This species occurs with the 



last, and is perhaps a state of it resulting from its complete spontaneous 

 division into tvi^o individuals by the contraction at the middle. 



5. Navicula . (PL 2, fig. 20.) This resembles the preced- 

 ing very much, but is a fresh-water species, occurring in ponds near 

 West Point, also in streams in Virginia. 



6. Navicula? striatula. (PL 2, fig. 21, a, i.) I refer to this genus 

 with much hesitation the very elegant and interesting species shown by 

 fig. 21 a, b. It is easily known by a set of peculiar and beautiful un- 

 dulating ridges, represented in the figure, and which give to the margin 

 of the form a ruffled appearance, in whatever position they are ob- 

 served. One of the faces (a) is lanceolate, the other (b) is somewhat 

 wedgeform, with both ends obtusely truncate. The lanceolate face 

 shows a set of fine lines apparently proceeding from the ridges above 

 referred to, and reaching nearly to the middle line of the face, I have 

 sometimes seen two individuals united laterally by their lanceolate 

 faces, producing a very beautiful form. All the individuals which I 

 have seen, have been free, Avithout pedicel, and when living, their spon- 

 taneous motions were very distinct. I have found it in a living state in 

 fresh-water ponds and streams near West Point, also in Mountain Run, 

 near Culpepper Court House, in Virginia ; and I detected it in a fossil 

 state among other fossil infusoria from Bridgewater, Mass. (See fio-s. 

 6 and 7, PL 20, of Plitchcock's Final Report on Geology of Massa- 

 chusetts.) 



In Pritchard's History of Infusoria, I find two figures repre- 

 senting A^. striatula, which leave no doubt that ours is the same 

 species. (See Hist. Inf. Pi. 3, fig. 137, 138.) The following 

 interesting remarks with regard to the organs of locomotion in 

 this genus, are also taken from this work. 



"In the small pools left by ebb of the tide near Cuxhaven, 

 Dr. Ehrenberg remarked numerous little bodies, apparently simi- 

 lar to Navicula [Surirella) elegans and N. striatula, but which 

 from their comparatively very great size and structure of lorica, 

 were easily distinguishable from the latter upon closer examina- 

 tion. One of these ribbed glass-like creatures was, besides its 

 size, remarkable for its great mobility, and Dr. E. was enabled 

 to investigate its system of locomotion much more satisfactorily 

 than he had hitherto done in any of the genus. This organ he 

 states was very different, both in form and size, to what he had 



