10 Algpe, Bncillariese, Rhaphidese, Navicukcese. Pleurosigma. 



3. Navicula aspera Ehr., Mikrog., t. 35 A, f. 5. De Toni, Syll. Alg., 33 

 II, p. 100. Stauroneis aspera Ehr., Amer., p. 134, t. II, f. 12, etc; 

 Castrac, Atti Acc. porit. N. Lincei, 18 Marzo 1877, p. 245. — Valvis 

 lineari-lanceolatis vel elliptico-lanceolatis, 100-180 == 25-26, apici- 

 bus obtusis vel subacutis; rhaphe zona angusta hyalina in vittam 

 cuneiformem hyalinam, margines valvse haud attingentem, circa no- 

 dulum centralem magnum rotundatum aut aegre visibilem ampliata 

 cincta; valvis adparenter punctis grossis obtectis, sub lente maxime 

 augonte striis subtilibus, longitrorsum interruptis, tenuiter trans- 

 verse divisis, regulariter atque ad apices valva3 radiantibus, circi- 

 ter 9-10 in 10 u..; facie connectivali lata, apicibus truncatis rotun- 

 datis, medio constricta. 



In tripoli ad Montes Labronicos Tuscicv (Castrac). 



4. Naviculadidyma (Ehr.) Kuetz., Bacill., p. 100, t. IV, f. 17, t. XXVIII, 34 

 f. 75. De Toni, Syll. Algar., II, p. 71. Castrac, Atti, Acc Pont. N. 

 Lincei, 18 Marzo, 1877, p. 245. Finnularia didijma Ehr., Amer., t. II, 

 IV, f. 3; Diploneis didi/ma Ehr., Mikrog., t. XXII, f. 60. — Valvis 

 ellipticis, medio constrictis, apicibus acutato-rotundatis, sulcis lon- 

 gitudinalibus rectis; striis moniliforraibus, adpressis, circiter 8 in 

 10 u., radiantibus vel subparallelis, rhaphem non attingentibus; 

 nodulo centrali e rotundato oblongo, plus minus distincto, area an- 

 gusta cincto. 



In tripoli ad montes Labronicos Tuscice (Castrac). 



5. Navicula elliptica Kuetz., Bacill., p. 98, t. 30, f. 55. De Toni, Syll. 35 

 Algar., II, p. 89. Navicula ovatis W, Sm., Br. Diat., I, p. 48, t. 17, 



f. 153. Castrac, I. c. p. 7. Pant., 1. c, p. 7. — Valvis ovali-elli- 

 pticis vel oblongo-ellipticis, 25-35 » 12-15; rhaphe valida, area hya- 

 lina subangusta, circum nodulum centralem abrupte ampliata cincta; 

 sulcis rhaphi quam maxime adproximatis, ambitum zonas hyalinfe 

 sequentibus; striis grosse punctatis, in medio valvte rectis, dein 

 magis magisque paullo radiantibus, circiter II in 10 j.. 



In marga pliocenica inferioro agri Spoletini UmbriaB (Castrac-). 



Gen. Pleurosigma W. Sm., in Ann. Nat, Hist , II, ser., Vol. 

 IX, p. 5. 



Frustula libera, naviculacea, elongata, e facie connectivali visa, 

 oblonga, linearia vel anguste lanceolata, nonnumquam late linearia et 

 medio constricta panduriformia, utroque fine truncata vel rotundata, 

 membrana connectivali semper recta angusta; valvae convexae, plus 

 minus sygmoidea^, rhapho plus minus sygmoidea donatse ; strife decus- 

 satse vel rectangulares, rhaphem subattingentes. 



