142 p. T. CLEVK, SYNOPSIS OF THE NAVICULOID DIATOMS. 



A. sejuneta Pant. (Ill PI. XXXV f. 495; 1893) probably the half valve of some Navicula, 

 belonging to the section Functatce. 



A. staurophora Pant. (Ill PI. XV f. 228; 1893). 



A. strigata Pant. (Ill PL XI f. 181; 1893). 



A. tertiaria Pant. (Ill PI. XV f. 225; 1893). 



A. transylvanica Pant. (Ill PI. I f. 12; 1893) similar to A. ovalis. but with a stauroid 

 centra] nodule. 



A. vittata Pant. (Ill PL XXII f. 32G; 1893) akin to A. ovalis? 



MastOgloia Thwaites (1848). 



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

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

 transverse punctate strise, usually subparallel, the puncta so disposed as to form obliquely decussa- 

 ting, or straight, or undulating, longitudinal, striee. Connecting zone not complex. Between the 

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

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

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

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

 mities. On staining with methylene-green a number of small, intensely co- 

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

 ;j|-l (Conf. A. S. Atl. PL CLXXXV f. 32). 



■_r$ '\ As early as 1833 one species of Mastogloia was named by Agardh 



;■ B-j Frustulia elliptica, and in 1844 another (probably M. lanceolata Thw.) was 

 t^^-j described by Kutzing (Bac. PL XXX f. 37) as Navicula meleagris. In 1848 

 ^CZ5i' 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 with between the mamillate mucous cushion constituting the nidus of this form, 

 cell-contents_;^500 times ^^^ ^^^ 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 iirst 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 Smith's view, are small cubical chambers or »loculi» opening 

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



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

 removed it to the Cocconeidse and created the Genus Orthoneis for elliptical cocconeiform species of 

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

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

 gloiacece, comprising Mastogloia, with the addition of the forms hitherto classed by him in Ortho- 

 neis; and Orthoneis, comprising only the forms with a few lunate loculi which he had before 

 placed in Stictoneis. 



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

 either in respect of the elliptical, or lanceolate, outlines, or of the fewer or greater number of the 

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



Considerable differences exist in the structure in Mastogloia, some species having decussating 

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



