142 



P. T. CLEVK, SYNOPSIS OF THE NAVICULOID DIATOMS. 



A. sejtmcta Pant. (III Pl. XXXV f. 495; 1893) probably the half valve of some Navicula, 

 belonging to the seetion Functatce. 



A. staurophora Pant. (III Pl. XV f. 228; 1893). 



A. strigata Pant. (III Pl. XI f. 181; 1893). 



A. tertiaria Pant. (III Pl. XV f. 225; 1893). 



A. transylvauicu Pant. (III Pl. I f. 12; 1893) similar to A. ovalis. biit with a stauroid 

 central nodule. 



A. vittata Pant. (III Pl. XXII f. 326; 1893) akin to .4. ovalis? 



MåstOgloia Thwaites (1848). 



Valve linear, lanceolate or orbicnlar, frequently with rostrate or capitate ends, symmetrical. 

 Median line usually undulate. Axial area usually indistinct. Central area small. Strueture: 

 transv^erse punctate strise, usually subparallel, the puncta so disposed as to form obliquely decussa- 

 ting, or straight, or undnlating, longitudinal, strite. Connecting zone not complex. Between the 

 zone and the valve there is a marginal septate plate. In conjugation two mothercells form two 

 auxospores (Ltiders Beob. p. 557). — Cell-contents (of 31. Smithii) have along the valves two chro- 

 matophore-plates, extending from the apices towards the central nodule. They have a narrow 

 sinus reacliing from the ends half-way to the centra. In F. V. the plates are bent near the extre- 

 mities. On staining vv^ith methylene-green a nuniber of small, intensely co- 

 loured plastids make their appearance at the surface-stratum of the plasma. 

 (Conf. A. S. Atl. Pl. CLXXXV f. 32). 



As early as 1833 one species of Mastogloia was named by Agakdh 

 Frustulia elUptica, and in 1844 another (probably M. lanceolata Thw.) was 

 described by Kutzing (Bac. Pl. XXX f. 37) as Navicula meleagris. In 1848 

 a third species was described by Thwaites (Ann. 2:d Ser. Vol. 1) under 

 the name Dickieia Dansei, but on W. Smith pointing out the great difference 

 Mastogloia Smithii wh\i between the mamillate mucous cushion constituting the nidus of this form, 

 magnified. ^^'^ ^^^ leaf-like fronds of Dickieia, Thwaites created the new Genus Masto- 



gloia for its reception and that of twO'additional species discovered by Smith. 

 W. Smith (S. B. D. Vol. II p. 63) was the first to call attention to the most characteristic 

 feature of the new Genus, viz the septate marginal plate attached, according to him, to the con- 

 necting zone. This plate can easily be isolated in preparation, and appears to be placed between 

 the zone and the valves. The septa, in Smitu's view, are small cubical chambers or »loculi» opening 

 outwards, which is probable, as in mounting they are frequently filled with air. 



In 1860 Grunow placed this Genus in the Naviculacese, but in 1867 (Nov. Exp p. 16) he 

 rémoved it to the Cocconeidie and created the Genus Orthoncis for elliptical cooconeiform species of 

 Mastogloia with a band of numerous loculi, and a subgenus Stictoneis for similar forms with a 

 few lunate loculi only. In 1880 (Aret. Diat. p. 17) Grunow formed a separate family, the Masto- 

 gloiacece, c(miprising Mastogloia, with the addition of the forms hitherto classed by him in Ortho- 

 neis; and Orthoncis, comprising only the forms witli a few lunate loculi wliich lie had before 

 placed in Stictoneis. 



As however I do not see sufficient generic difference between Mastogloia and Orthoneis 

 either in respect of the elliptical, or lance(date, outlines, or of the fewer or greater numberofthe 

 lunate, or rectangular, loculi, I propose here to unite them in one Genus, Mastogloia. 



Considerable differeuces exist in the strueture in Mastogloia, some species haviug decussating 

 lines of puucta, while others have the puncta in traiisverse and longitudinal rows. Transitions, 



