Bacillariese, Naviculacese, Pleurosigma. 231 



4. Staurosigma Ovulum Rabenh. FI. Eur. Algar. I, p. 353. — Valvis 1000 

 oblongo-ovatis vel ovoideo-ellipticis, 35-45 u.. longis, sub polis le- 

 viter constrictis, apicibus subproductis rotundatis, area media ad^ 

 valvarum rnarginem extensa et plerumque dilatata; striis trans- 

 versis subradiantibus, rectis, rhaphen vix attingentibus, 20-22 in 

 10 p. 



Hab. ad litora maris atlantici septentrionalis (L. Rabenhorst). 



Species Pleurosigmatis forte huic generi adscribenda : 

 Pleurosigma staurophorum Grun. in Cl. et Gr. Arct. Diat. p. 61. 



PLEUROSIGMA W. Sm. [1853] in Ann. Nat. Hist. II ser., vol. IX, p. 5, 

 Br. Diat. I, p. 61 (Ktym. plaura latus et sigma littera S), Rabenh. 

 Fl. Eur. Algar. I, p. 230, Grun. in Wien. Verh. 1860, p. 555, Cl. 

 et Gr. Arct. Diat. p. 48, Van Heurck Syn. p. 114, De-Toni Os- 

 serv. tasson. Bacill. p. 896, Peragallo in Diatomiste 1891 (in litteris), 

 Gyrosigmatis et Naviculce sp. auct., Endosigma Breb. [1849] in 

 D'Orb. Dict. XI, p. 418. — ■ Frustula libera *), naviculacea, elonga- 

 ta, e facie connectivali visa oblonga, linearia vel anguste lanceo- 

 lata, nonnumquam late linearia et medio constricta panduriformia, 

 utroque fine truncata vel rotundata, metnbrana connectivali semper 

 recta, angusta; valvee convexae, plus minus sigmoideae, rhaphe plus 

 minus sigmoidea donatae; strise decussatae vel rectangulares, rha- 

 phen subattingentes. 



Sectio I. Strise decussatae [secus tres directiones sese intersecantes]. 



Subsectio A. Striae omnes fere rcqualiter delicatae. 



* Species aquse subsalsse vel marinse incolse (nonnunquam etiam fossiles). 



1. Pleurosigma angulatum (Quek.) W. Sm. in Ann. Nat. Hist. 1. c. 100 i 

 p. 7, t. 1, f. 8, Br. Diat. I, p. 65, t. 21, f. 205, Rabenh. Fl. Eur. 

 Algar. I, p. 234, H. L. Sm. Sp. T. n. 389, 390, Gruu. et Cl. Arct. 

 Diat. p. 51, V. H. Syn. p. 115, t. 18, f. 2-4, Truan Diat. Astur. 

 p. 48, t. 3, f. 1, Perag. Pleuros. t. 5, f. 3-5, Navicula thuringica 

 Kuetz. Bacill. p. 102, t. 4, f. 27 (nomen anterius !!), Navicula angulata 

 Quek. On Microscope 1848! p. 438, t. 8, f. 4-7, Gyrosigma thu- 

 ringicum Rabenh. Siissw. Diat. p. 47, t. 5, f. 27. — Valvis late lan- 

 ceolatis, circ. 150 u.. longis, leniter curvatis, sigmoideis, parte me- 



*) Frustula plerumque libera, rarissime intra tubulos mucosos, Schizone- 

 matis ad instar, inclusa (Cfr. Pleurosigma eximium et P. scalproides) 



