268 Bacillarieae, Naviculaceae, Rhoicosigma. 



rhoicos arcuatus et sigma), Achnanthosigma Reinh. [1882] Bacill. 

 weiss. Meeres p. 298 c. icone, teste Grun. in Botan. Centralbl. 1883, 

 I, p. 321-322, De Toni 1. c. p. 896, Pleurosigmatis, Toxonidece et 

 Donkinice sp. auct. — Frustula e facie connectivali visa achnan- 

 thiformi-arcuata, valvae dissimiles, superior convexa rhaphen re- 

 ctam vel vix incurvam, superficie appositam praebens, inferior con- 

 cava rhaphen arcuato-sigmoideam carinatam ostendens. 



Obs. Pleurosigmati proximum genus, Rhoiconeidi quodam- 

 modo analogum sed in Rhoiconeide rhaphe recta est. 



1. Rhoicosigma COmpactlim (Grev.) Grun. in Cleve Diat. fr. West. Ind. n25 

 Archip. 1878, p. 9, Arct. Diat. p. 54, Pleurosigma compactum 

 Grev. in Micr. Journ. V, p. 12, t. 3, f. 9 (valva inferior), Bonkinia 

 compacta (Grev.) Ralfs in Pritch. Inf. p. 921 saltem ex parte, 

 Rhoicosigma Reichardtii Grun. in Micr. Journ. 1877, p. 181, t. 195, 



f. 19 (valva superior), Rhoicosigma Rheichardtianum Grun. in 

 Hedwigia 1867, p. 19. — Frustulis e facie connectivali visis 75- 

 175-20-50, medio leniter constrictis, subarcuatis, valvis oblongis, 

 superiore maxime convexa, nodulo centrali rotundato, rhaphe sub- 

 recta vel paullo incurva, superficiali, valva inferiori concava, rha- 

 phe valde incurva carinataque; striis transversis 15-20 (vel paullo 

 ultra), longitudinalibus 20-24(-28) in 10 u. 



Hab. in mari adriatico, rarissime (D. Reichardt); ad insulas 

 Virginum, raro (Cleve); an ad littora Bahusiae eadem species? 

 (Lagerstedt). — Color frustuli exsiccati plus minus saturate 

 flavus. 



2. Rhoicosigma Weissflogi Grun. in Cl. et Grun. Arct. Diat. p. 54, 1126 

 Perag. Pleuros. t. 9, f. 23-24. — Habitu Rhoicosigmatis com- 

 pacti, valvis 118-134 » 18-19, rhaphe valde arcuata, utrinque per 

 longum spatium cum marginibus convexis coincidente; striis acute 

 definitis ut in Pleurosigmate {Rhoicos.)sulcato medio fere sub angu- 



lo recto intersectis, 13-14 in 10 p.., apices versus sub angulo acuto 

 intersectis; striis transversis multo magis confertis, paullo conspicuis. 

 Hab. ad insulas «Seyschellen». 



3. Rhoicosigma oceanicum Perag. m litt. et Pleuros. t. 10, f. 5-6. — 1127 

 Rhoicosigmate compacto Grun. plerumque majus et paullo magis 

 sigmoideum , striis vero minus delicatis , longitudinalibus 23-24, 

 transversis 17-18' in 10 u. 



Hab. ad « La Rochelle, Meulon, Cannes »; etiam inter algas mu- 

 scum Corsicce constituentes. — Cfr. var. Perag. 1. c. 1. 10, f. 10-15. 



