Mr. J. Ralfs on the Diatomacese. 105 



transverse strice ; lateral surfaces striated, contracted near the 



ends. Ehrenberg, Die Infus. p. 202. t. 20. f. 7 ; Pritch. Infus. 



p. 219. f. 180—182. Fragiluria striatula, A^. Syst. p. 7 ; Kutz. 



in Linnaea 1833, p. 73 ; Grev. in Br. Fl. vol. ii. p. 403 ! F. Car- 



michaelii, Harv. Br. Alg. p. 198. Grammonemn striatula, Ag. 



Consp. Diatom, p. 63. 



" Appin, Capt.Cannichael ;" Southampton, Miss Hill; co. Antrim, 

 Ireland, Mr. W. Thompson. 



I have dl•a^^^l up my description of this plant from one of Capt. 

 Carmichael's specimens given nie by Mr. Harvey. 



At first sight this plant bears so great a resemblance to Sfria- 

 tella arcuata as to appear merely a variety of it ; and without 

 taking into consideration the lateral form, it would be difficult to 

 find a good distinguishing character. 



From my specimens I was unable to ascertain a\ hcther the fila- 

 ments were attached or not ; they are fragile, and here and there 

 cohere at their angles in the same manner as Striatella arctiata. 

 The fr^istules are generally not so broad in projjortion to their 

 length as those of Striatella arcuata, but, like them, have nume- 

 rous series of transverse striae, w^hich however in this plant are 

 not so strongly marked, and under a low^ power especially are less 

 evident than the marginal striae. 



The lateral surfaces arc swollen in the centre and constricted 

 near the ends, with numei'ous transverse striae along their whole 

 length. 



P.S. Since the above description was ^vi-itten, I have gathered 

 this plant on the muddy sides of rocks in Sw ausea Bay, 



The filaments are more slender than in the Appin specimen, 

 of a dirty-brown colour, much cm-led and entangled, and but 

 slightly fragile. 



In di-ying it adheres much more firmly to paper than does the 

 Striatella arcuata, is less fragile, does not turn green in drying, 

 and has no gloss. 



Plate II. fig. 1. a, Tessella catena ; b, lateral view ; c, lateral view with 

 the septa removed. 



Tetracyclus, n. g. 

 Filaments free, fragile, fom'-sided, each side roimded and form- 

 ing the segment of a distinct circle ; frustules longitudinally 



striated. 

 1, T. lacustris. Fru.etules about twice as broad as long ; lateral sur- 

 faces with from seven to nine distinct transverse strife. 



Llyn Prefeddyr near Barmouth, the Rev. T. Salwey ; pool near 

 Dolgelley*. 



In xAugust last this plant w^as sent to me by Mr. Salwey, who 

 found it sparingly among Fragilaria hyemalis in the above lake. 

 * I have this year met with it in two or three pools near Dolgelley. — J. R. 



