BRITISH DIATOMACE^E. 93 



45. Navicula Rostellum, W. Sm. V. elliptical-oval ; extremities 

 produced into distinct rostra; striae 80 in -001". Length of V. 

 •0015". Breadth of V. -0007". v.v. 



Navicula apiculata, Greg. Mic. Jour. vol. 4. pi. i. 13. 



Freshwater. Grasmere, August 1853, W.Sm. Falls of the Tummel, July 

 1854, Dr. Greville. 



The name N. apiculata has been appropriated by M. De Brebisson (Diat. 

 Cherb. fig. 5) to a marine species quite distiuct from the present. 



46. Navicula Hennedyii, n. sp. Valve elliptical, subacute, or ros- 

 trate at the extremities ; marginal band of equal breadth through- 

 out ; striae 24 in -001". Length of valve -0029" to -0042". Breadth 

 of valve -0016" to -0024". v.v. 



Marine. Frith of Clyde, January 1854, Mr. Hennedy. Poole Bay, Sep- 

 tember 1854 ; Stomach of Pecten, Kinsale Bay, April 1855, W. Sm. Lyme 

 Regis, Dorsetshire, 8 fathoms, November 1855, Mr.Capron. 



47. Navicula Lyra, Ehr. Valve elliptical, subacute or rostrate; 

 striae in a marginal and two central bands ; marginal band of 

 unequal width; striae 20 in -001". Length of valve -0036" to 

 •0064". Breadth of valve -0018" to -0026". v.v. 



Ehr. in Kutz. Bacill. xxviii. 55 ; Sp. Alg. p. 74. N. elliptica (N. Smithii, 

 Breb.), sporangial? Synop. pi. xvii. 152 a*. 



Marine. Salt Pans, Hampshire, September 1 854, W. Sm. Cumbrae, Janu- 

 ary 1854, Dr. Arnott. 



The last two species are almost identical in form ; but the arrangement of 

 the striae in each is peculiar, and constant under every shape and size of the 

 individual frustule. In N. Hennedyii the marginal stria?, form a continuous 

 band of equal width along the circumference of the valve, and the unstriated 

 portion of the surface, between the border and the linear longitudinal bands 

 that lie along the median line, is, in consequence, of unequal width, having the 

 outline of a segment of a circle. The unstriated portion of N. Lyra is, on 

 the contrary, almost linear, and the marginal band of stria? has the outline of 

 a segment of a circle slightly inflated at the centre of its base : in both the 

 striae are beautifully moniliform, though the character is more apparent in the 

 last : both species occur with the extremities sometimes subacute and some- 

 times rostrate. 



48. Navicula humerosa, Breb. Valve nearly linear, or slightly 



