of Microscopical Org-anisms. 345 



Infusoria, as somewhat larger and more coarsely marked, 

 with the puneta arranged in circles, which I have not 

 observed in this specimen, but in other respects they agree 

 exactly. It is strongly punctate as at (i, but shows no 

 signs of striae. 



Hab. Para River. 



Fig. 77. NiTscHiA MESOLEPT^, BcuL, nov. sp. ? Small, 

 linear in side view, with acute apices ; two rows of pune- 

 ta approaching at the middle ; striae wanting or obscure ; 

 valves tapering from the centre to the slightly dilated, 

 acute apices. 



Hab. Para River. 



This form, under the name above given, was doubtfully 

 marked as a variety of Nitschia linearis of Smith. It 

 seems, however, to me, to be distinct in structure, and the 

 latter is a fresh-water form. 



Fig. 78. The scale here represented was found accom- 

 panying the original sketches, and I believe applies equally 

 to all the figures, except perhaps to those of Coscinodiscus ? 

 tenuis, and the lateral view of Polymyxus. As the original 

 proofs have been almost exactly reproduced, and the iden- 

 tical specimens could not always be found, I have been 

 unable to verify the measurements. This scale is, I be- 

 lieve, equally magnified with the other figures. 



I have now described as accurately as it is possible to do, 

 from specimfens which have been six years mounted in bal- 

 sam, without fresh and free species to compare, the new and 

 doubtful forms contained in this remarkably rich locality. 

 The great bulk of the soundings consists, as I have before 

 said, of the beautiful Polymyxus coronalis. Of the other 

 species, Cyclotella Kutzing'iana ? Biddulphia tenuis, trina- 

 cria, &c., and the different Surirellas, are among the more 

 common forms ; Ditylum and Si/ringidiuni are by no means 

 rare, while Navicula, Pinnularia, and Coscinodiscus also 



JOURNAL B. S. N. H. 44 



