14 DONKIN, ON DIATOMACEyE. 



SO long ago as tlie montli of June, 1857, at a time, in 

 short, when neither Mr. Athey nor any one else in this country 

 knew that marine diatoms were to be found on the sands in 

 such localities. 



Navicularetusa, DeBreb. (fig. 17). — Form on F. V. oblong, 

 angles rounded, constricted in the middle ; S. V. linear, nar- 

 row, extremities rounded. Valve convex near the margin ; 

 strise parallel, costate, subdistant, short, not reaching to 

 the median line, shortest opposite the central nodule ; me- 

 dian line delicate ; middle third of valve hyaline. Length, 

 from -0020" to •0025' ; breadth, about -0004". 



Concerning this form, much confusion prevails amongst 

 observers. I have thought it necessary to give a figure of it, 

 to show more clearly the points of difi'erence between it and 

 N. truncata and N. Northumbrica, to which it is closely allied. 

 The description I have above given of N. retusa corresponds 

 with that of Prof. Smith, given in the appendix -lo the 

 ' Synopsis,' and also with the description of the S. Y. given 

 by De Brebisson ; it difi'ers from its nearest allies, especially 

 in the linear outline of its S. V., in its short thick strise, cut 

 short at a considerable distance from the median line, so 

 that the middle third of the valve is hyaline. The F. V. 

 figured by De Brebisson {' Diat. Litt. de Cherl.,' fig. 6) be- 

 longs to a diflferent species — to N. truncata — although his 

 delineation of the S. V. is correct in outline. 



What the late Professor Smith meant by N. pectinalis, 

 Breb., is now somewhat uncertain. According to Professor 

 Arnott, it was unknown to Dc Brebisson ('Microscopical 

 Journal,' vol. vii, p. 177) ; its strise, according to Smith's 

 description, are 16 in '001", and therefore as coarse 

 as those of N. retusa, but much coarser than those of 

 N. truncata and N. Northumhrica. Professor Arnott, how- 

 ever, appears to be acquainted with N. pectinalis, and 

 would confer a benefit on the science by describing and 

 figuring it. ^ , %<^- % 



15. Amphiprora fulva, n. sp., Donkiri [' Trans, Micro. 

 Soc. Lond.,' n. sp., vol. vi, PL III, fig. 4H)v— Form on F. V. 

 oblong, extremities rounded, gradually and deeply constricted 

 in the middle ; S. V. narrow, lanceolate, apiculate ; valve 

 slightly alate, compressed laterally ; median line straight ; 

 strise transverse, fine, probably 60 in -001" ; dry valve of a 

 rich salmon colour. Length, from -0050" to -0055". 



In my previous contribution (op. cit.), I described and 

 figured the F. V. of this species as that of PI. lanceolatum ; 

 but I have since discovered that, in doing so, I have com- 

 mitted an error, and use the present opportunity of correct- 



