38 p. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



slightly excentric towards the ends. Transv. and obi. striae 25 in 0,oi mm. — P. lUUc. W. Sm. 

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



Brackish water: North Sea! Caspian Sea (Grun.), Eed Sea (G-run.)! Massachusetts'! Hondu- 

 ras (Grun.). 



Var. obtusiuscula Grun. Ms. — More obtuse. L. O.ies; B. 0,oi95 mm. Strife 22,5 in 0,oi mm. 



Marine: Granton Quarry (Grun.). 



Var. africana Grun. (1879). — L. 0,i8 to 0,i9; B. 0,oi4 to 0,oi8 mm. Transv. and obi. strise 

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



Brackish water: South Africa! 



Var. americana Cl. — L. 0,28; B. 0,02 mm. Transv. and obi. strise 19 in 0,oi mm. 



Brackish water: Quincy, Mass.! 



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

 the acute ends. L. 0,i3 to 0,38; B. 0,024 to 0,03 mm. Median line central, slightly sigmoid. 

 Transv. and obi. striae 17,6, "/jg, "">/„, 2o/,g, 2fl/,g in 0,oi mm. — W. Sm. Ann. M. Nat. H. [2] IX 

 p. 6 PI. I f. 4. B. D. I, Pl. XX f. 199. Per. Ill f. 5 to 8.; P. angulatum var. elongat. V. H. Syn. 

 p. 115 PI. XVIII f. 7. P. elongatum var. gracilis Grun. Casp. Sea Alg. p. 115 Pl. Ill f. 7. Per,. 

 II f. 20, 21. 



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

 nean Sea! Adriatic! Java! Sumatra! China! Tahiti! Halle in Saxony! Baltic! Caspian Sea (Grun.) 

 Medoc (Per.). 



Var. gracilescens Grun. (1880). — V. very narrow, gently sigmoid, with acute ends. L. 0,204 ; 

 B. 0,016 mm. Median line central. Transv. and obi. striae ^*"Vi6.5 ^^ f>oi ^^- ~ ^- ^T^^'Cilescens 

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



Marine: Seychelles (Grun.). 



P. elongatum is very nearly akin to P. delicatulum, but the transverse striae 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. delicatulum with the striation of P. 

 elongatum (specimens frgm Java and Sumatra have the form of P. delicatulum and transv. obi. 

 striae ^0/,,, "/„). 



Var. fallax Grun. (1880). — V. gently sigmoid, narrow linear or lanceolate. L. 0, 1 to 0, 1 7 ; 

 B. 0,022 to 0,024 mm. Median line sigmoid; central. Transv. and obi. striae 2%„, 2*/22, *V2i ™ 

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



Marine: Finmark, Sea of Kara (Grun.), Sumatra (Deby coll.)! 



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

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



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

 central. Transv. and obi. strise ^'/igi "^o i^ *5'0i °i°i- ~ ^- ^elic. var.? kariana Grun. A. D. p. 50 

 Pl. in f. 69. P. Jcarianum Per. p. 6. 



Marine: Sea of Kara (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 obi. striae "/^j, 

 *7i6- "At in 0,01 mm. — Cl. D. of Arct. Sea p. 19 Pl. Ill 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. and obi. striae i*/,, 

 (Per.) '7,3 in 0,oi mm. — P. decorum var. americ. Per. p. 5 Pl. I f. 9. 



Marine: Connecticut! 



