KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 26. N:0 2. 45 



46. P. formosum W. Sm. (1852). ^ V. narrow, linear-lanceolate, gently sigmoid, gradually 

 and unilaterally narrowed towards the ends. L. 0,i4 to 0,53; B. 0,02 to 0,05 mm. Median line 

 sigmoid, excentric, generally for a considerable distance coincident with the convex margin. Oblique 

 striae crossing each other at an angle of 90°. Transv. and obi. striae "/j^, 'Vhi "Vie inO.oi mm. — 

 W. Sm. Ann. M. Nat. H. [2] IX p. 5 PL I f. 1. B. D. p. 63 PI. XX f. 195. Grun. A. D. p. 48. 

 V. H. Syn. p. 116 PL XIX f. 4. Per. I f. 3 to 5. P. australicum 0. Witt. Mus. GodefF, p. 70 

 PL Vni f. 7 (1873). P. decorum W. Sm. I p. 63 PL XXI f. 196. Grun. A. D. p. 49. V. H. Syn. 

 p. 116 PL XIX f. 1. Per. I f. 11 to 13. P. tahUense 0. Witt. Mus. GodeiFr. p. 67 PL VIU 

 f. 13 (1873). 



Marine: North Sea! Mediterranean Sea! Ked Sea! Java! China! Behrings Island! Sandwichs 

 Islands! Galapagos Islands! West Indies! 



Var. dalmatica Grun. (1880). — V. narrow, slender, acute, slightly sigmoid. L. 0,25 to 0,32; 

 B. 0,03 mm. Median line slightly excentric. Transv. and obi. striiB i^/,2, '7u ^^ ^'O' ™™^- — 

 P. decor, var. dalm. Grun. A. D. p. 49. Per. II f. 6 to 9?. Icon. n. PL IV f. 21. 



Marine: Balearic Islands! Adriatic (Grun.)! 



Var. (Ehoicosigma) Arcus Cl. — V. arcuate. L. 0,2; B. 0,02 mm. Transv. and obi. strise "/is 

 in 0,01 mm. — PL IV f. 18. 



Marine: Macassar Straits (Grove Coll.)! 



Var. balearica Per. (1891). — V. linear, with unilaterally rounded ends. L. 0,35 to 0,54; B. 

 0,034 to 0,06 mm. Transv. and obi. striee '^/g, '*/g, ''/g in 0,oi mm. — Per. p. 4 PL I f. 6, 7. 



Marine: Mediterranean Sea (Per.), Singapore (Grove Coll.)! 



Var. longissima Grun. (1880). — V. lanceolate, sigmoid. L. 0,4 to 0,78; B. 0,085 to 0,073 mm. 

 Median line sigmoid, excentric at the ends. Transv. and obi. striae 'Vio- '*/n> 'Vio, '7i3) "An i^ 

 0,01 mm. — Grun. A. D. p. 48. Per. p. 4 PL I f. 1, 2. 



Marine: Puerto Caballo (Per.), Colon! Campeachy Bay! Samoa! China! Java! Galapagos 

 Islands! 



All the forms from P. speciosum are very nearly connected and might be united into one 

 single species, characterized by the oblique striae crossing each other at an angle of about 90°. 

 Between P. formosum and P. decorum there is absolutely no specific difference, and by numerous 

 varieties P. formosum graduates into P. pidcJirum and P. speciosum. By the var. dalmatica P 

 formosum is connected with P. subrigidum, P. longiim and P. Peragalli, which latter is intermediate 

 in the passage to P. Nubecula. — Donhinia reticulata Norm. (Grev. in T. Bot. Soc. Ed. vol. VIII 

 p. 237 PL III f. 13, 14. Pritch. Inf. 1861 p. 921) is probably akin to the last described species. 

 It is a large form (L. 0, 1 6 mm.) with very excentric median line and highly carinated valves. 

 Oblique striae about 8 in 0,oi mm. This form, found in Western Australia, is entirely unknown 

 to me. A somewhat similar form occurs in Oamaru deposit but I have seen only some incomplete 

 specimens. L. 0,2. Striae 10 in 0,oi mm. 



Toxonidea Donkin (1858). 



Valve asymmetrical, thin. Median line arcuate, excentric. Axial area indistinct. Central 

 area indistinct. Structure the same as in Pleurosigma. Zone not complex. 



This genus comprises asymmetrical forms of Pleurosigma. The cell-contents are not known, 

 but will probably offer some interesting peculiarities. 



1. T. insignis Donk. (1858). — V. strongly asymmetrical, with almost straight dorsal and 

 very convex ventral margin. Ends subrostrate. L. 0,i2 to 0,13; B. 0,0 2 5 to 0,03 mm. Median 

 line strongly excentric, coincident at the ends for some distance with the dorsal margin. Transv. 



