146 SKETCH OF THK INFUSORIA 



Virginia ; and I detected it in a fossil state among other fossil infu- 

 soria from Bridgcwater, Mass. (See figs. G and 7, pi. 20, of Hitch- 

 cock's Final Ilcport on Geology of Massachusetts.) 



In Pritchaid's history of Infusoria, I find two figures repre- 

 senting N. striatula, which leave little doubt that ours is the same 

 species. (Sec 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 

 before noticed in that genus. Instead of a snail-like expanding 

 foot, loTig" delicate threads projected ivhere the ribs or transverse 

 marks of the shell join the lateral portion of the ribless lorica, 

 and ivhich tJie creature voluntarily dreio in or extended. An ani- 

 malcule one eighteenth of a line long, had twenty-four for every 

 two plates, or ninety-six in the total ; and anteriorly, at its broad 

 frontal portion, four were visible. It is probable that this creature 

 may form the type of a special group of the BacUlariae." 



7. Navicula . (PI. II, fig. 22.) This small species of Navi- 

 cula with striate faces, is not uncommon in the infusorial stratum of 

 Richmond, Va. 



b. Without transverse striae. 



8. Navicida . (PI. II, fig. 23, a, b.) This species is distin- 

 guished by having two grooves which cross each other at right angles 

 on the ventral face, presenting a cruciform appearance, and dividing 

 this face into four equal portions, which are without striae. It is a 

 conspicuous species in many American specimens of fossil fresh- 

 water infusoria, and is very common in the hving state. I have 

 found it in New York, Ouisconsin and Virginia. 



