MEMORANDA. 93 



markings on the Ceratoneis fasciolata {Pleurosigma fasciold), 

 by means of using a l-8th-inch object-glass, which power 

 I presume he considered necessary for that purpose. I have 

 now the pleasure of stating that with the same kind of con- 

 denser, but with one of Powell's recently-made l-4th-inch 

 objectives, I have brought out the markings of this species in 

 the most satisfactory manner; also tvitJi the same poicer \he 

 markings, rather difficult of detection, of the Pleui'osicjma 

 delicatulum, intermedium, mibicula and ^shtarii, and of Nitz- 

 schia siqmoidea, using, however, in place of the achromater, 

 Shadbolt's Annular Condenser, with the light direct from the 

 lamp — a method of illumination which seems to be especially 

 adapted to the demonstration of delicate test objects. The 

 same result has been obtained, but I think in a more perfect 

 manner, by means of the prism furnished by Powell and Lea- 

 land, which should be so adjusted for this purpose as to give 

 the object illuminated on a perfectly black field. 



The above facts may be interesting to some of your readers, 

 should you deem them worthy of insertion in the next number 

 of your Journal. — E. Bleakley, M.D., Norwich. 



New Species of Uiatomacese. — The species of Diatomaceae 

 here described as new, together with others, were detected 

 either as parasites upon Algae, or entangled in mud adhering 

 to shells. Algae, &c., brought home by the Exploring Expe- 

 dition under the command of Capt. Wilkes, U.S.N. 



1. Amphitetras favosa , Harvey et Bailey. Loricis tabulari- 

 bus ; lateribus vix concavis, primario ; secundario quadran- 

 gulo, angulis fere rectis vix productis, superfice cellulis magnis 

 hexagonis tessellata. Hah. Mindanao. 



2. Amphitetras Wilkesii, H. et B. ; loricis prismatico-tabu- 

 laribus, lateribus concavis, primario longitudinaliter striato- 

 punctato medio transversim zonato ; secundario quadrangulo, 

 angulis productis rotundatis, superficie cellulis minutis in 

 lineas simplices furcatasque dispositis notata, prominentiis 

 iugalibus punctulatis. Hab. Puget's Sound. 



3. Aulacodisciis Orcgaiius, H. et B. ; lorica prominentiis 

 redecim intramarginalibus instructa, a quibus tot radii fere 



ad umbonem procurrent ; superficie praeter umbonem glaberfi- 

 mum, minute punctata iridescente. Hah. Puget's Sound. 



4. Campi/Iodiscus Kiitzingii, H. et B. ; sellaeformis, late 

 marginata, sulcis subquinquaginta transversis continuis curvatis 

 impressa. Hah. Mindanao. 



5. Cocconeis pai'mtda, H. et B. ; late elliptica, linea media 

 longitudinali notata, utroque latere costis (vel sulcis) trans- 



