KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 26. X:0 2. 4.S 



the ends. Central area rather large, irregularly rhomboid. Tran.sv. and obi. striee "/j., '7i6' '"/u' 

 "/i8> 'Vio in 0,01 mm. — P. quadratum var.? rhombeum GtRUN. A. D. p. 50. P. rhomb. Pee. Ill 

 f. 13, 14. 



Marine: Java! Labuan! Port Jackson! Aukland (Grun.), Samoa! China! Oakland, California! 



P. rhombeum greatly resembles P. qiiadratiuii and angulatum, but differs by the more ex- 

 centric median line and the coarser striation. 



36. P. obscuriim W. Sm. (1852). — V. narrow linear, with unilaterally narrowed and 

 rounded ends. L. 0,09 to 0, 15; B. 0,oi mm. Median line strongly asymmetrical, near the ends 

 close to the curved margin. Transv. and obi. strife equidistant, 25 (Per.) to 29 (W. Sm.) in 0,oi 

 mm. — W. Sm. Ann. M. Nat. H. [2] IX p. 8 PL I f. 11. B. D. I p. 65 PL XX f. 206. Per. I 

 f. 14, 15. P. macilentum Pbe. p. 13, PL V f. 24 (1891). 



Marine: England (W. Sm.), Balearic Islands (Per.). 



Var. harbadensis Cl. L. 0,14 to 0,i8; B. 0,oi5 mm. Transv. and obi. strife 'V20' ^"Ai 

 in 0,01 mm. 



Marine: Barbados! 



37. P. (Rhoicosigma) falcatum Douk. (1861). — V. linear, with unilaterally narrowed and 

 rounded ends. L. 0,i5 to 0, is; B. 0,oi5 mm. Median line flexuose in the middle, strongly ex- 

 centric, following the curved margins of the ends. Strise fine, oblique. — Donk. M. J. I p. 7 PL I 

 f. 1. Ehoic. falcat. Grun. Hedw. VI p. 20 (1867). Per. IX f. 25, 27. 



Marine: Northumberland (Donk.). 



Doubtful; specimens in Grove's collection are Gyrosigma arcticum Cl. 



38. P. (Rhoicosigma?) incertum Per. (1891). — V. slender, sigmoid, acute. L. 0,.33; B. 

 0,019 mm. Median line slightly sinuose, very excentric towards the ends. Transv. and obi. strisB 

 "'/']7 in 0,0 1 mm. — Per. p. 32 PL IX f. 21. 



Marine: Atlantic coast of North America! 



39. P. (Rhoicosigma) Weissflogii Grun. (1880). -- V. linear, with unilaterally narrowed 

 and rounded ends. L. 0, iis to 0,134; B. 0,oi8 to 0,oi9 mm. Median line excentric, and strongly 

 sigmoid, closely following the curved margins for a considerable distance. Median oblique striae 

 cross each other in an angle of 90°; the terminal more acute. Transv. and obi. strise '^Vis ih 0,oi 

 mm. — Ehoic. Weissfl. Grun. A. D. p. 54. Per. IX f. 23, 24. 



Marine: Seychelles (V. H. colL)! 



40. P. umbilicatum Cl. N. Sp. — V. linear, with unilaterally rounded and very slightly 

 rostrate ends. L. 0,o6.5 to 0,10; B. 0,oi5 mm. Median line strongly sigmoid, for a long distance 

 closely following the convex margin of the valve. Central area unusually large, transverse and 

 rounded. Transv. and obi. strise equidistant, 22 in 0,oi mm. — PL IV f. 22. 



Marine: Labuan! 



This species is in form nearest to P. Weissflogii, but differs by the large area, and the 

 close striation. 



41. P. Exsul Cl. N. Sp. — V. linear-lanceolate, gently sigmoid, with subacute ends. L. 0,i8 ; 

 B. 0,018 mm. Median line strongly sigmoid and excentric, enclosed between two longitudinal lines. 

 Central nodule small, rounded. Transv. and obi. striae ^2/23 i^ ^jOI ^^™- — P^- ^ ^- l^- 



Marine: Gulf of Naples (Deby Coll.)! 



This species, of which I have seen only one specimen, has the outline of P. formosum, but 

 has much closer striation, and longitudinal lines close to the median line. 



