38 P. T. Cr.EVE, SYNOPSIS OF TLK NAVICDLOID DIATOMS. 



slightly excentric towards the ends. Transv. and obl. strise 25 in 0,o i mm. — P. delic. W. Sm. 

 Ann. Mag. Nat. H. [2J IX p. 6 Pl. I f. 5. B. D. I p. 64 Pl. XXI f. 202. Per. p. 13 Pl. V f. 20 to 22. 



Brackish water: North Sea! Caspian Sea (Grun.), Red Sea (Grun.)! Mas.saclm.setts! Hondu- 

 ras (Grun.). 



Var. obtusiuscula Grun. Ms. — More obtu.se. L. 0,165; B. 0,0195 mm. Stria; 22.5 in O.oi mm. 



Marina: Granton Quarry (Grun.). 



Var. africana Grun. (1879). — L. O, is to 0,19; B. 0,oi4 to 0,0 ig mm. Transv. and obl. stria; 

 23/.^4 in 0,01 mm. — Grun. in Cl. M. D. N:o 197. 



Braekisli water: South Africa! 



Var. americana Cl. — L. 0,28; B. 0, 02 mm. Transv. and obl. strite 19 in 0, 01 mm. 



Brackish water: Quincy, Mass.! 



16. P. eloiigatum "W. Sm. (1852). — V. slightly sigmoid, elongated, gradually attenuate to 

 the acute ends. L. 0, 13 to 0,38; B. 0, 024 to 0, 03 mm. Median line central, slightly sigmoid. 

 Transv. and obl, stri* i*/,^, 'V,8, '-"Ar, "7,8- ■"/\9 in 0,oi mm. — W. Sm. Ann. M. Xat. H. [2] IX 

 p. 6 Pl. I f. 4. B. D. I, Pl. XX f. 199. Per. Ill f. 5 to 8.; F. avgulatum rar. doii/jaf. V. H. Syn. 

 p. 115 Pl. XVIII f. 7. P. elongatnm var. (jradlis Grun. Casp. Sea Alg. p. 115 Pl. III f. 7. Per. 

 II f. 20, 21. 



BrackLsh water: Spitsbergen! North Sea! Atlantic coast of North America! Mediterra- 

 nean Sea! Adriatic! Java! Sumatra! China! Tahiti! Halle in Saxony! Baltio! Ca,spian Sea (Grun.) 

 Médoc (Per.). 



Var. gracilescens Grun. (1880). — V. very narrow, gently sigmoid, with acute ends. L. 0,2 04 ; 

 B. 0,016 mm. Median line central. Tran.sv. and obl. strife '*"Vib.5 i^ 0, 01 mm. — P. gracilescens 

 Grun. A. D. p. 50. Per. p. 7 Pl. in f. 9. 



Marine: Seychelles (Grun.). 



P. elongatum is very nearly akin to P. clelicafuluni, but tlie transverse striie are a little 

 closer than the oblique and it has a perfectly central median line. Still these characteristics 

 seem not to be constant, as I have forms of the shape of P. clelicatulnm with the striation of P. 

 elonqatum (specimens from Java and Sumatra have the form of P. delicatulum and transv. obl. 

 striaj 20/^,, 19/,,). 



Var. fallax Grun. (1880). — V. gently sigmoid, narrow linear or lanceolate. L. 0,i toO,i:; 

 B. 0,022 to 0,024 mm. Median line sigmoid, central. Transv. and obl. strije -''.,1,. -""..o, -' -j, in 

 0,01 mm. — Grun. A. D. p. 50 Pl. III f. 66. Per. II f. 23. 



Marine: Finmark, Sea of Kära (Grun.), Sumatra (Deby coU.)! 



Specimens from Sumatra are much more narrow than the fig. in A. D. and resemble greatly 

 P. delicatulum, but have the median line perfectly central. 



Var. hariana Grun. (1880). — L. 0,2 to 0,21; B. 0,02 to 0,022 mm. Median line perfectly 

 central. Transv. and obl. strise -^/,9, -%o in 0,oi mm. — P. delic. var.? Icariana Grun. A. D. p. 50 

 Pl. III f. 69. P. karianum Per. p. 6. 



Marine: Sea of Kära (Grun.). 



This form connects P. elongatum with P. longum. 



17. P. longum Cl. (1873). — V. narrow, linear-lanceolate, .slightly sigmoid. with acute 

 ends. L. 0,i8 to 0,3; B. 0,oi8 to 0,021 mm. Median line central. Transv. and obl. stria? ''',5, 

 '7i6> ^Vi7 in 0,01 mm. — Cl. D. of Aret. Sea p. 19 Pl. III f. 14. Grun. A. D. p. 49 Pl. III f 71. 

 Per. II f. 2. 



Marine: Greenland! Spitzbergen! 



Var. americana Per. (1891). — V. narrow lanceolate, with acute ends. L. 0,35 to 0,4; B. 

 0,02 to 0,025 mm. Median line very slightly excentric at the ends. Transv. niid obl. striiu 

 (Per.) "/i5 in 0, 01 mm. — P. decormn var. amcric. Per. p. 5 Pl. I f. 9. 



Marine: Connecticut! 



IS 



