42 p. T. PLEVE, SYNOfSlS OF THE NAVICULOID BIATOMS. 



29. P. Brunii Cl. (1891). — V. linear, strongly sigmoid, suddenly attenuated to the acute 

 ends. L. 0,4 2 to 0,4.5 ; B. 0,3 1 to 0,033 mm. Median line central. Central nodule small. Trans- 

 and oblique strise "/jj in 0,oi mm. — Per. p. 16 PI. VI f. 8. 



Marine (pelagic): Bay of Bengal! Java! 



30. P. jayanicum Grun. (1878). — V. narrow, lanceolate, gently sigmoid, acute. L. 0,i25 

 to 0,144; B. 0,019 to 0,022 mm. Median line nearly central in the middle, excentric towards the 

 ends. Transv. and obi. strife equidistant, about 28 in 0,oi mm. — R angulatum var. jav. GrRUN. 

 in Cl. M. D. 145. P. javanicum Geun. A. D. p. 52 (1880). Per. V f. 10. 



Marine (pelagic): Java! China! 



This species has the outline of P. strigosum, but is thinner (dry, yellowish) and more acute. 

 It is most nearly akin to P. acutum. As P. hyalinmn, Grunow describes in A. D. (p. 52) a similar, 

 pelagic form from Triest (L. 0,085; B. 0,oio5 mm.), the striation of which is too delicate for measuring. 



31. P. acutum Norm. (1861). — V. lanceolate, gently sigmoid, acute. L. 0,24 to 0,3; B. 

 0,0 2 to 0,0 2 8 mm. Median line sigmoid, very excentric towards the ends. Transv. and obi. strise 

 '"/■n- "As. "/an in 0,0 1 mm. — Norm. Pritch. Inf. p. 920. Per. Ill f. 1, 4. P. acutum var. austral- 

 asicum Grun. in Cl. M. D. 286 (1882). 



Marine (pelagic): Europe (Norm.), Croisic (Per.), Java (Deby Coll.)! St Vincent, Australia! 

 Yeddo Bay (Brun Coll.)! 



This species is nearly akin to P. javanicum and P. Stuxbergii, from which latter it differs 

 by its less acute oblique strise and the excentricity of its median line towards the ends. The fig. 2 

 in Peragallo's monograph has the outline and median line of P. Stuxbergii, but the striation of 

 P. acutum. The iig. 3 in the same monograph is another, allied form, described here as P. pelagicum 

 Per. and formerly mistaken by me for P. acutum var. australasicum Grun., which latter now seems 

 to me to be identical with P. acutum. 



32. P. (Ilhoicosigma?) mnroccanum Cl. (1891). — V. narrow, lanceolate, gently sigmoid, 

 gradually attenuated to the acute ends. L. 0,2 to 0,3; B. 0,02 to 0,o37 mm. Median line some- 

 what excentric, sigmoid. Transv. and obi. strise "/is' ^7]9 in 0,oi mm. Angle about 70'. — Bhoico- 

 sigma marocc. Per. p. 32 PL IX f. 22. 



Marine: Marocco! Gulf of Naples! 



This form is doubtful as a species and requires further examination. 



33. P. aestuarii Br]Sb. (1849). — V. lanceolate, gently sigmoid, with slightly rostrate ends. 

 L. 0,07 to 0,08; B. 0,oi7 mm. Median line more sigmoid than the valve, excentric. Transv. and 

 obi. striae equidistant, 19 to 21 in 0,oi mm. — Navic. cest. KtJTZ. Sp. Alg. p. 890. P. cast. W. Sm. 

 B. D. I p. 65 PL XXXI f. 275. Grun. A. D. p. 52. Per. p. 12 PL V f. 11 to 13. P. candidum 

 ScHOM. Preuss. D. II Nachtr. PL IT f. 57 (1867). P. angulatum var. cest. V. H. Syn. p. 115 

 PL XVIII f. 8. 



Marine: North Sea! Adriatic (Grun.), Caspian Sea (Grun.), California! 



This species has the striation of P. angulatum but, by the flexure of the median line, seems 

 to be nearer akin to P. lanceolatum. 



34. P. latum Cl. (1880). — V. rhomboid-lanceolate, slightly sigmoid, gradually tapering to 

 the subobtuse ends. L. 0,074 to 0,o85; B. 0,02 mm. Median line slightly sigmoid, excentric towards 

 the ends. Transv. and obi. strise ^y^j in 0>oi mm. — Cl. A. D. p. 14, 51 PL III f. 68. 



Marine: Finmark! California! 



This form requires a closer examination. 



35. P. rhombeum Grun. (1880). — V. rhomboidal, sigmoid, often angular in the middle, 

 and with obtuse ends. L. 0,i2 to 0,2 6; B. 0,o3 to 0,0 7 mn^. Median line strongly sigmoid towards 



