64 BRITISH DIATOMACEjE. 



line of the valve, as given at 341 /3 ; this accidental modification 

 is, however, hardly entitled to rank as a variety. The fronds in 

 Mastogloia are rather the aggregated mamillae of consolidated mucus 

 formed around each frustule, than envelopes common to many, and 

 their greater or less dimensions greatly depend upon the stage of 

 growth and locality. On moist rocks, the aggregated frustules form 

 a gelatinous and tenacious stratum, while, on water plants, each 

 frustule adheres independently to the Alga on which it grows. The 

 frustule itself is ordinarily eccentric to the mucus developed around 

 it, and sits as it were on the summit of a little nipple-like cushion of 

 gelatine : see fig. 341 x 100. 



1. Mastogloia Danseii, Thw. Valve elliptical; loculi 8 to 20 ; stria? 

 42 in -001". Length of frustule -0015" to -0020". Breadth of valve 

 •0005". v.v. 



Mastogloia Danseii, Thwaites in literis, Oct. 14, 1848. Dickieia Danseii, 

 Thw. in Ann. Mar. 1848, 2nd ser. vol. 1. pi. xii. K. Prit. Anim. xxiv. 30. 



Brackish water. Banks of the Tamar, Devonshire, Mar. 1848, Mr. Dansey. 

 "Little Sea," Dorsetshire, Oct. 1848 ; River Ouse, Sussex, Oct. 1852, W. Sm. 

 Near Belfast, Oct. 1850, Dr. Dickie. Breydon, Norfolk, Sept. \854,Mr. Wigham. 

 Cumhrae Island, Oct. 1854, Mr.Hennedy. 



This species was first determined by Mr. Thwaites in the spring of 1848, 

 and assigned by him to the genus Dickieia of Ralfs ; he soon, however, saw 

 reason to doubt the accuracy of placing it in that genus, and upon my sup- 

 plying him with two additional species, constituted the genus Mastogloia for 

 their reception. This course was taken in consequence of the character of the 

 frond in the present genus presenting a mamillate, and not a uniform surface 

 as in Dickieia: had Mr. Thwaites been acquainted with the peculiar structure 

 of the frustule in Mastogloia, he would have seen an additional and stronger 

 reason for placing it apart. 



Supp. Plate LXII. 388. 



2. Mastogloia lanceolata, Thw. Valve lanceolate, elliptical, extre- 

 mities acute ; loculi 8 to 30 ; stria? 42 in *00l". Length of frus- 

 tule -0011" to -0026". Breadth of valve -0006" to -0008". v.v. 



Thw. in lit., Oct. 1848. Navicula Meleagris, Kiitz. Bacill. xxx. 37? 



Brackish water. " Little Sea," Dorsetshire, Sept. 1848 ; Poole Bay, Sept. 

 1851 ; Lancing, Sussex, July 1854, W. Sm. Isle of Arran, Aug., and Isle 

 of Cumbrae, Oct. 1854, Dr. Arnott. Newbie Deposit, Prof.Harkness. 



