43(J APPENDIX. 



latter, upon closer examination. One of these ribbed oval 

 glass-like creatures, which belonged to the genus Navicula, 

 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 dif- 

 ferent, both in form and size, to what he had before 

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

 foot, long delicate threads projected where the ribs or 

 transverse marks of the shell join the lateral portion of the 

 ribless lorica, and which the creature voluntarily drew in or 

 extended. An animalcule 1- 18th 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. 

 The openings for the purposes of nutrition appeared to 

 be at the extremity. Whether these organs were super- 

 numerary, and existed along with cirri, &c., and the flat 

 snail-like foot, which the rest of the Navicula possess, could 

 not be determined. Longitudinal clefts at the broad side 

 of the shell were not present, but as many as ninety-six 

 lateral openings for the exit of the cirri were perfectly 

 distinct. It is probable this creature may form the type 

 of a special group of the Bacillaria. Of one thing Dr. E. 

 is convinced, that the Naviculae in general are very dif- 

 ferently constituted individually; thus, in some cases, the 

 six round openings in the little shell are distinctly visible, 

 whilst in others clefts, which in some cases gape, and are 

 unprovided with circular openings, are all that can be 

 made out. 



