The Surirelloideæ are usually understood to include the genera Surirella, Podocystis, Cymatopleura and Campylodiscus, all of which resemble each other more or less, either in having a keel or markings like the divisions of the keel in Surirella and a median line, or pseudoraphe. The genus Nitzschia also has a keel, but it does not border each side of the valve as in Surirella, being found either near one margin or between it and the centre. Certain of the Surirellæ are allied to the group Tryblionella of the Nitzschiæ, while forms of Stenopterobia are distinguished with difficulty from the group Sigmata. The following arrangement, therefore, is intended to include all genera having a keel or something which resembles it. _Hantzschia._--Valve asymmetrical; keels of the two valves opposite each other. _Nitzschia._--Valve asymmetrical; keels not (usually) opposite each other. _Surirella._--Valve usually symmetrical; a keel on each border. _Cymatopleura._--Valve without an elevated keel, but with markings like those of Surirella; undulated in zone view. _Campylodiscus._--Valves saddle-shaped. HANTZSCHIA GRUN. (1877) (named after C. A. Hantzsch) Valve arcuate, with rostrate ends; keel puncta short, prolonged into costæ or extending across the valve; median nodule rudimentary; the keels of the two valves opposite each other. Distinguished from Nitzschia chiefly by the position of the keels. According to Mereschkowsky, however, two species of Nitzschia, N. lanceolata and N. spectabilis, show the same peculiarity. Chromatophores four, two on each of the zones (Mereschkowsky). HANTZSCHIA AMPHIOXYS (EHR.) GRUN. Valve slightly arcuate, with rostrate apices; keel puncta, 8 in 10 µ; striæ transverse, 16-18 in 10 µ, punctate. L. 60 µ. Quite variable. Fresh water. Pl. 32, Fig. 9. {114}HANTZSCHIA AMPHIOXYS VAR. MAJOR GRUN. Valve as in type, but the keel puncta are 5 in 10 µ and the striæ are 11-12 in 10 µ. L. 71 µ. H. amphioxys var. major Grun. is stated to be 120 µ in length. The present form is smaller but corresponds in puncta and striation. Van Heurck remarks that it approaches H. virgata. Abundant in sand ripples on the beach at Cape May, N. J. Pl. 39, Fig. 4. Fig. 6, Pl. 39, is drawn from an authentic specimen of Wm. Smith's Nitzschia amphioxys, from England, and is introduced for comparison. The central nodule is not evident. Fig. 3, Pl. 39, is from a specimen from an unknown locality. The keel puncta are 6 and the striæ 16 in 10 µ. HANTZSCHIA VIRGATA (ROPER) GRUN. Valve arcuate on the dorsal side, nearly straight on the ventral side, with rostrate, recurved apices; keel puncta prolonged to one-third the width of the valve, 4 in 10 µ; transverse striæ, 9-10 in 10 µ. L. 115 µ. Shark River, N. J. (Kain). I have not been able to find this form on our coast. The figure is drawn from a specimen from another locality. Pl. 32, Fig. 23. HANTZSCHIA MARINA (DONK.) GRUN.