236 NKIDIUM. 



N. Hyalosira Cleve. (in Le Diat, i., p. 77, pi. 12, f. 11*), plate 

 27. fig. 786. 



Valve convex, thin, lanceolate, rostrate or with rounded apices ; striae 

 punctate, 29 in 1 c.d.m. Frustule quadrangular, connecting zone with 

 numerous pleats. Length, about 2 c.d.m. Frustule feebly silicious. 



Marine. Month of the Tay, Scotland (Cleve and Moller, No. 309 !) Cresswell, Northumber- 

 land, England (Deby.). 



Neidium Pfitzer. (1S71. Ueber Bau und Entw. d. Baa, p. 39). 



This very natural group corresponds to my Affines ; it is based on the 

 form of the endochrome, on the apices of the raphe near the central nodule 

 being turned in opposite directions, on the striation of the valve being often 

 oblique, and on this striation being frequently interrupted by one or more 

 longitudinal sulci. 



Pinnularia Ehr. (1840). Valve furnished with costae and not 

 striae. This genus corresponds to my group Pinnularia. Former authors 

 also included in it the Radiosce, whose striae could not then be resolved into 

 beads. 



Rhaphidodiscus Th. Christian (1887, in the Journal "The 

 Microscope," p. 67). 



This genus is, according to Mr. Deby, based on the 

 accidental position of a Navicula in a valve of Melosira. It 

 is also perhaps founded on a disciform Navicula, such as 

 that represented in Fig. 33 at the side. This figure, which 

 corresponds very well with that of Mr. Christian, is drawn 

 from one of my photographs, and reproduces a valve 

 found by Mr. Weissfiog in material from Naparima in the 

 ^. ./ig. 33. j slan( j f L a Trinite, Antilles. 



Discnorm Aavicula. 



Lately, Prof. Brun, having been good enough to lend me the photographs 

 and preparations which he received from Mr. Christian, I have been able to 

 assure myself that the Naparima diatom in no wa> differs from that of Mr. 

 Christian's specimen, which is a genuine Navicula. Mr. Deby's explanation 

 is the only one that satisfactorily explains the figure published by Mr. Christian. 

 We have reproduced this as figure 913 on plate 35. 



Schizostauron Grun. (1867, in Hedwigea, p. 28). 



A genus containing eight species, all from the South of Europe, or Extra- 

 European. Round the central nodule is a blank space, stauroneiform (or a 

 true stauros ?), bifurcated into a St. Andrew's cross. 



Stauroptera Ehr. (1843). 



Group including all forms possessing a pseudo-stauros. 



Stictodesmis Grev. (1863), South Pac. Diat., p. 30.). 

 Based on the craticular state of the valve, analogous to Craticula. Fig. 34 

 represents Stictodesmis Australis Grev., the most common form of this genus. 



