Note on Pedalion intra. 215 



of estremest angle, however, let one precaution be taken, viz. that 

 balsam be used above the shde and balsam below ! The case will 

 then correspond to that given in the diagram. 



Of course in practice the upper convex surface of the front lens, 

 or system, has a curvature and distance to positively and consider- 

 ably refract the transmitted rays, but the case I have given is the 

 easiest elucidated. 



Boston, August 2%id, 1871. 



IV. — Note on Pedalion mira. By C. T. Hudson, LL.D. 



In my paper on Pedalion mira, in the September number of the 

 ' Microscopical Journal,' I purposely omitted to give any sketch or 

 detailed account of the internal structure of this new and singular 

 rotifer, for I had not had time enough to investigate it thoroughly ; 

 but as some doubt has been expressed as to whether Pedalion is a 

 rotifer at all, I wish to state that it has a trilobed mastax, with a 

 manducatory apparatus similar to that of Triarthra, and the usual 

 convoluted tubes carrying at least two vibratile tags on each side, 

 though most probably there are more. I have not seen any con- 

 tracticle vesicle; but then I have equally failed to see it in 

 Triarthra, in which rotifer, as well as in Pedalion, either the dense 

 corrugated walls of the posterior extremity of the stomach overlie 

 the vesicle, or the vesicle itself (as in Pterodina) is evanescent, 



Pedalion s muscles are, for its size, enormous; at least two 

 broad and coarsely striated muscles run transversely round the body 

 below the neck, and the longitudinal muscles for retracting the 

 trochal disk are unusually powerful, 



I had intended in the course of September to complete my 

 investigation of Pedalion s structure ; but the creatures diminished 

 in number rapidly throughout August, and have now, I believe, 

 entirely disappeared — to return, I hope, next summer. 



V. — Another Hint on Selecting and Mounting Diatoms. 



Communicated by Capt. Fred, H. Lang, President of the Beading 



Microscopical Society. 



My paper "On Selecting and Mounting Diatoms," read to the 

 members of the Eeading Microscopical Society in October, 1870, 

 and published in the December number of the ' Monthly Micro- 

 scopical Journal,' has been, I have every reason to believe, of con- 



