of British species of the genus Pleurosigma. 9 



inch, greatest breadth of ditto ^|^ of an inch. Transverse 



striae -^^^-^q of an inch apart [v. s.). 



Hull, Mr. R. Harrisonl 



A very distinct species, notable for its graceful form and 

 strongly marked transverse striae. 

 Plate II. fig. 4. Valve of P. Strigilis. 



11. Pleurosigma acuminatum^ mihi. Valve broadly lanceolate, 

 much attenuated towards the extremities : colour a light brown. 

 Average length of the valve y^^ of an inch, greatest breadth 

 of ditto 12^0 ^^ ^^ i^^^- ^^^^^ irJUTTo ^^ ^^ ^^^^ ^P^^** (^- ^O- 



Navicula sigma, Ehr. 1833 ; Pritchard, Hist, of Animal, pi. 3. fig. 146. 

 Nav. acuminata, Kiitz. Linn. 1833 ; Bacill. p. 102. tab. 4. fig. 26 ; 

 Phy. Ger. p. 95 ; Sp. Alg. p. 86. 



Shoreham Harbour, 1850. 



I have Prof. Kiitzing's authority, in a letter dated July 1851, 

 for the synonyms of this species, which has occasionally been 

 confounded with the N. Hippocampus of Ehrenberg by British 

 microscopists. It differs from it in habitat, in colour, in the 

 delicacy of its striae, and in its form, which is more slender and 

 attenuated. 

 Plate II. fig. 5. Valve of P. acuminatum. 



12. Pleurosigma Fasciola, mihi. Valve lanceolate, extremities 

 produced, flexure considerable: colour very pale. Average 

 length of valve ^Iq of an inch, greatest breadth of ditto j-g^j 

 of an inch. Striae jj^qo ^^ ^^ ^^^^ apart {v. v.). 



Ceratoneis Fasciola, Ehr. ; Kiitz. Bacill. p. 104. tab. 4. fig. 4 ; Phy. 

 Ger. p. 96 ; Sp. Alg. p. 88. 



On the mud of tidal harbours. Belfast Bay, 1849. Poole Bay, 

 1850. Coast of Sussex, 1850. Hull, Mr. B. Harrison ! 



I have restored this species to the same genus as its allies, the 

 elongation of its valves not appearing to require its separation, 

 and the more careful examination of its surface showing the 

 central and terminal enlargements of its median line characteristic 

 of the true Naviculece. 



Plate II. fig. 6. Valve of P. Fasciola. 



13. Pleurosigma prolongatum, Yi. sip. Valve much elongated, very 

 narrow lanceolate; flexure moderate; striae obscure: colour very 

 pale. Average length of valve y^ ^ of an inch, greatest breadth 

 of ditto ^yoo °^ ^^ ^^^^ (^' ^•)- 



Poole Bay, 1849. 



