14 THE DIATOMACE^: OF PHILADELPHIA AND VICINITY 



MELOSEIRA AG. (1824), em. DE TONI (1892) 

 (melos, a limb or member, and seira, a chain) 



Frustules globose, ellipsoidal or cylindrical, concatenate, closely joined together. Valve 

 either simply punctate or punctate and areolate. A constriction of the cell-wall, forming a 

 furrow between the edge of the valve and the girdle, is more or less evident. 



The genus Meloseira constituted by Agardh has been variously modified by Kuetzing, 

 Thwaites, Wm. Smith, Van Heurck, De Toni, and others. In Systema Algarum Agardh 

 included certain species of Conferva, of Lyngbye, Dillwyn and others, and limited his genus to 

 frustules more or less globose (fila articulata ad genicula constricta), although in his Con- 

 spectus Criticus (p. 64), he modifies the description (fila teretia articulata, articulis diametro 

 aequalibus vel longioribus) to include M. varians. As, however, Lysigonium Link, Gaillon- 

 ella Bory, and other genera enlarged by Ehrenberg and Kuetzing, came to be included under 

 Meloseira, Thwaites- suggested the division of the genus into two: Orthosira, in which the 

 frustules a,re not convex at the ends and Aulacosira in which no central line is apparent but 

 with two distinct sulci. Wm. Smith adopts the genus Orthosira but rejects Aulacosira, 

 including all forms under the former genus and Meloseira, suggesting that differences "exist 

 in the formation of the sporangia" of the two genera. M. varians and M. crenulata appear 

 to form auxospores or sporangial frustules in different ways, as will be noticed hereafter. 



As, however, the present state of our knowledge is so limited and as much confusion 

 would result in further changing the nomenclature, I shall adopt, for the most part, the divi- 

 sion made by De Toni, separating Gaillonella and Lysigonium and employing the name Melo- 

 seira as emendated in Sylloge Algarum, although, as stated, it omits the species of Agardh. 

 That a further division may be necessary is indicated by the differences existing between the 

 Orthosira forms and the others. 



ANALYSIS OF SPECIES 



Frustules cylindrical and lengthened: 



Valves with two distinct furrows; granules small distans 



Valves with coarse granules granulata 



Valves denticulate on the margin crenulata 



Valves denticulate and constricted roeseana 



Valves with row of large puncta on the girdle side undulata 



Frustules cylindrical and compressed: 

 Valves punctate and areolate sulcata 



The chromatophores consist of circular and compressed or irregular flat granules which 

 lie along the wall of the cell. 



MELOSEIRA DISTANS (EHR.) KtJETZ. 



Frustules cylindrical, slender, with two furrows, one on each side of the suture; valve in 

 zone view with fine puncta in longitudinal rows; puncta in valve view scattered. L. 7-10 ft. 

 Meloseira nivalis Wm. Sm. 

 Coscinodiscus minor Wm. Sm. 

 Fresh water. Fossil in New England deposits. 

 PL 1, Figs. 8 and 9. 



NOTE. In all species of Meloseira, as well as Gaillonella and Lysigonium, the frustules 

 are so closely coherent that when the filaments are broken entire frustules are less frequently 

 found than a union of two valves of contiguous frustules. 



