Valve with fine, transverse striæ; on the margin, puncta at intervals; terminal nodules distinct.
May's Landing, N. J.
Pl. [12], Figs. 16, 17, 18.
Fig. 17, from Tom's River, N. J., is an approach toward A. brasiliensis Grun.
Fig. 18 represents the frustules geminate, a frequent occurrence.
NAVICULOIDEÆ
In discussing the Naviculoid group, the general divisions of Cleve are here followed, and all diatoms having a true raphe are included. I have added the genus Epithemia and also Rhopalodia, partly because they contain a raphe of a certain kind and partly because they resemble the markings of certain of the genus Hantzschia in the following group, although in other respects there is probably no similarity.
The difficulty of combining the numerous genera into groups which are naturally affiliated is avoided in the following arrangement based on superficial similarities, and is intended merely as an artificial key. To unite all forms having a raphe and which are symmetrical with valves similar and not sigmoid, under the one genus Navicula, as has been the custom previous to the publication of Cleve's monograph, would result in associating species differing in so many respects in relation to structure of the valve and cell contents that it seems advisable to retain the new genera, especially as the original genus is likely to be still further reduced when more is known of the structure and life history of the group.
KEY TO THE GENERA
| Valves dissimilar. Achnantheæ | |
| symmetrical | Cocconeis |
| asymmetrical | |
| to the longitudinal axis | Anorthoneis |
| to the transverse axis | Rhoicosphenia |
| in zone view | Achnanthes |
| Valves similar and asymmetrical | |
| asymmetrical to the longitudinal axis | |
| valves parallel | Cymbella |
| valves not parallel | Amphora |
| valves keeled, twisted (sometimes symmetrical) | Amphiprora |
| valves keeled | Tropidoneis |
| valves reniform and keeled | Auricula |
| median line sigmoid at the ends | Scoliotropis |
| asymmetrical to the transverse axis | |
| striæ punctate and costate | Gomphoneis |
| striæ punctate | Gomphonema |
| Valves similar, symmetrical and sigmoid | |
| striæ oblique | Pleurosigma |
| striæ at right angles | Gyrosigma |
| Valves similar, symmetrical, not sigmoid | |
| striæ punctate, nodules elongated | Frustulia |
| striæ subtly punctate, central nodule forked | Amphipleura |
| striæ punctate and reticulate, in two strata | Dictyoneis |
| striæ punctate and alveolate, in three strata | Trachyneis |
| striæ punctate, in two strata | Brèbissonia |
| striæ interrupted by blank lines | Anomœoneis |
striæ crossed by longitudinal lines | Caloneis |
| striæ oblique, median fissures in opposite directions | Neidium |
| striæ punctate and costate, median line with horns | Diploneis |
| striæ punctate; valves separated by septate plates | Mastogloia |
| striæ punctate, central area dilated into a stauros | Stauroneis |
| striæ punctate, area without stauros or horns | Navicula |
| striæ costate, not punctate | Pinnularia |