THALASSIOTHRIX. 32 I 



A. formosa Hassall. (Microscopical examination of the Water 

 supplied to the Inhab. of London, 1850; T.M.S., i860, viii., p. 149, pi. 7, f. 

 8 ; H.V.H. Atl., pi. 51, f. 19 and 20*), plate 11, fig. 439. 



Valve narrowly linear, diminishing somewhat in breadth from the base, 

 which is very strongly capitate, to the superior apex, the head of which is 

 much smaller ; stria? fine, about 17 in 1 c.d.m., interrupted by a very narrow 

 pseudo-raphe and a rather large hyaline area in the basal inflation. Girdle 

 face strongly inflated at the inferior portion, very slightly so at the superior 

 portion. Length, 7 to 10 c.d.m. 



Fresh water. The type-form has not yet been found in Belgium, but it has been found in 

 England (Kitton, Comber, Roper, Norman, Arnott.), Scotland (Baxter Coll., 2790), Ireland 

 (O'Meara), France, and Denmark. 



var. gracillima (Hantzsch) Grun. (H.V.H. Atl., pi. 5T, f. 22*; 

 Type No. 345), plate 11, fig. 440. 



Valves much narrower than in the type-form. 



Rather common at Antwerp in the town ditches and neighbouring waters. England, 

 Denmark, Ireland (O'Meara). 



var. infiata. (H.V.H. Atl., pi. 51, f. 23*; in Type No. 345), plate 

 11, fig 441. 



Girdle face abruptly inflated in its inferior third. 



Antwerp, mixed with the preceding. Denmark. 



var. Blcakeleyi. (A. BleakekyiVI. Sm. ! ; H.V.H. Atl., pi. 52, f. 1*), 

 plate 30, fig. 838. 



Frustules short, enlarged, dilated at the base. Length, 4-5 to 5 c.d.m. 



Marine Harwich (Bleakeley), Norfolk (\V. Sm.. ! Kitton), East Coast (Norman). 



var. Ralfsii. (A. Ralfsii. W. Sm.). 



Frustule still shorter and relatively broader than the preceding. 

 Length, 3-5 to 4-5 c.d.m. 



Fresh water. England (W. Sm., Norman). 



GENUS 43. THALASSIOTHRIX. CLEVE AND 



GRUN. (1880). 



Valves quadrangular, with apices unequally developed, margins 

 furnished with spines or elevated points, between which are seen 

 short marginal striae. 



x 



