112 P. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



median line of the latter. T have proposed (1883 Vega p. 474) to include these forms in a Section 

 Vegir, bnt I now prefer to connect them with the other species of iV. orthostichce. 



17. N. porto-montaiia Cl. N. Sp. — V. broad, liiiear, sliglitly gibbous in the middle, with 

 broad ronnded ends. L. O.ot; B. 0,oi7 mm. Median line with approximate median pore.s and 

 bordered by a narrow silicions rib. Terminal nodules thick, terminal fissures indistinct. Trans- 

 verse strise 19 to 20, longitudinal 19 in 0,oi mm. The puncta close to the median line are 

 larger than the others. — Pl. III f. 36. 



Fresh water: Puerto Monte, Chile, fossil (Kinker Coll.)! 



Gyrosigma Hassall (1845). 



Valve more or less elongated and sigmoid. Central nodule small. Ends of the median line 

 in contrary directions. Central area small or indistinct. Axial area indistinct. Strnctnre: puncta 

 disposed in transverse and longitudinal rows. — Cell-contents (of the freshwater forms) with two 

 chromatophores along tlie connecting zone, which long before the division of the cell are trans- 

 versely cut off and migrate in pairs to the inside of the valve. The opening between the halves 

 of the chromatophores becomes oblique, and each half increases to a chromatophore. The margins 

 of the chromatophores entire (Pfitzer, Bau und Entw. p. 57). Marine species (G. balticnm) have 

 irregularly serrated chi'omatop]iores the indentations being directed towards the central nodule. 

 The median part of the chromatophores is obliquely striate, their substance being alternately 

 thicker and tliinner. The striffi of the two chromatophores cross each other in an oblique angle 

 (O. Muller Ber. d. Deutch. Bot. Ges. 1883 p. 481). 



The sigmoid NavicnlcB were named Navieida Sigma by Ehrenberg. Hassall proposed for them 

 tlie name Gyrosigma, which was adopted by Rabenhorst (Die Siiss-vv. Diat. 1853), but not by other 

 diatomists, who prefered the newer name Pleurosignia, formed Ijy W. Smith, 1852, who publi.shed the 

 first monograph of the species (Ann. Nat. Hist. 2 ser. IX p. 1). The genus Pleurosigma, as accepted 

 by all diatomists, includes forms with a structure of small puncta or alveoli, disposed in transverse 

 rows, which are crossed by other rows, either longitudinal, or obliquely decussating. There are no 

 intermediate forms between these two types, and I think they may justly be considered as different 

 genera. For the forms witli the puncta in transverse and longitudinal rows, I adopt the name 

 Gyrosigma, although, as Grunow remarks, this name involves tautology. For the forms with tiie 

 puncta disposed in transverse and oblique rows I reserve the name Pleurosigma. — Among the forms 

 of Gyrosigma are several with carinated valves, for which Ralfs 1861 (Pritch. Inf. p. 920) proposed 

 the generic name Donkinia. In my opinion this genus is not acceptable, as founded on a cliarac- 

 teristic which is subject to too much variation. The same may be the case with Rhoicosignia, pro- 

 posed 1867 by Grdnow (Hedwigia VI p. 10) for forms with genuflexed or arcuate frustules. The 

 genus Rhoicosignia seems at first sight to be better fouiuled, as the valves of the same frustule 

 of R. compadum are (as Peragallo has shewn) dissimilar. But on the other hand some forms 

 (as jR. rohusfum) have evidently similar valves. Besides, the flexure of the frustule diifers in 

 different species to all degrees. The manuscript-name Endosigma Bréb. for the forras living like 

 Schizonema, in gelatinous tubes is not admissible, on the same grounds as Schizonema, Colleto- 

 nema, Endostauron etc. — From Gyrosigma maj' be removed Pleurosignia staurophonoii Grun., 

 which has no close affinity to any of the other forms, but has the chai'acteristics of Caloneis, being 

 a sigmoid form of that genus. — The division of the sigmoid forms of Xavicula into two groups, 

 founded on the disposition of the puncta in transverse and longitudinal, and in transverse and 

 oblique, rows, was first proposed by "VV. Smith, and has been accepted by all låter diatomists. 

 In the year 1880 Grunow published (in Arctische Diat.) an elaborate monograph, in which he 



