MEMORANDA. 139 



left alone. 1 should think that a prism with only one re- 

 flecting surface would he much more easily worked than one 

 with two. A prism of the latter form, however, is spoiled 

 by the slightest clipping of the edge ; while, in the arrange- 

 ment I have proposed, the edge does not come into use — and 

 it might perhaps be found more advantageous in the working 

 to have the edges truncated. — P. Gray, 7, St. Paul's Villas, 

 Camden Town, N.W. 



On the Rarer and Undescribed Species of Diatomace^e. 

 By T. Brightwell, F.L.S. Part II. 



ERRATA ET CORRIGENDA. 



I regret to find the following errors have crept into my 

 last paper which need correction. 



Page 94, line 4, insert reference to plate " (PL VI, fig. 15)." 



„ 94, „ 8, /or "fig. 15," read "18." 



„ 94, „ 4 from bottom, instead of "Aulacodiscus" read "Auliscus 

 sculptus = A. caelatus, Bailey." 



„ 95, line 1, for " Aulacodiscus," read " Eupodiscus." 



„ 95, ,, 6, "Aulacodiscus lcer,is." I find this form has been named 

 and distributed by Dr. Arnott as " A Kitloni" the specific name 

 of " Icevis" must, therefore, be cancelled, and " Kittoni " substi- 

 tuted. 



„ 95, line 19, the specific name should be " co&cinodiscus" instead of 

 " pyxidicula." 



„ 96, Hue 6, for " 019 to 0-3," read " "0019 to -0030." 



One general error runs through all the measurements ; they require au 

 additional '0 in front. 



description of plates. 

 Plate V. 

 Fig. 2, insert specific name " trilingulatus" 

 „ 4, for " pyxidicula" read " coscinodiscus." 

 „ 5, for " Aulacodiscus" read " Auliscus." 

 „ 6, insert specific name " coronatus." 

 „ 7, „ „ „ " marginatus" 



„ 9, ,, „ „ " cervinus." 



„ 10, for " Aulacodiscus" read " Eupodiscus" 



Plate VI. 



Pig. 11, insert specific name "radiata." 

 „ 12, „ „ „ " se hi i planus." 



„ 13, „ „ „ " Kiltoni." 



„ 15, „ „ „ " spinosa." 



„ 16, „ „ „ " stylorum." 



„ 17, for " Eupodiscus" read " Actinoptychus inter punctatm." 



