(dim. of actin, a ray) Frustules solitary, or in small clusters, sub-cuneate or nearly linear. Valve arcuate, rounded at one end and suddenly widened at the other into a cup-shaped or lychnoid inflation. ACTINELLA PUNCTATA LEWIS 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. {55}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