Valve linear, with rounded apices; striæ subtle; pseudoraphe indistinct. Marine. Cape May. Pl. 10, Fig. 37. Fig. 36 is an indeterminate form occasionally found in the blue clay. FRAGILARIA CAPUCINA VAR. MESOLEPTA RAB. Valve linear, constricted at the hyaline middle; apices slightly produced; striæ, 17 in 10 µ. Quite variable in size. Schuylkill River. Morrisville (Keeley). Pl. 10, Fig. 34. FRAGILARIA HARRISONII (WM. SM.) GRUN. Frustules rectangular, solitary or in twos. Valve cruciform; pseudoraphe narrow, lanceolate; striæ robust, radiating in the middle, composed of confluent puncta, larger at the circumference. Blue clay. Pl. 10, Fig. 31. FRAGILARIA CONSTRUENS (EHR.) GRUN. Valve in general outline lanceolate, with produced apices; pseudoraphe lanceolate, distinct or broad; striæ subtle, 15 in 10 µ. L. of valve, 10-45 µ. _Staurosira construens_ Ehr. _Odontidium tabellaria_ Wm. Sm. Blue clay. Pl. 10, Fig. 30. FRAGILARIA PARASITICA (WM. SM.) Frustules solitary or in twos. Valve lanceolate, sometimes constricted in the middle; pseudoraphe wide, lanceolate; striæ subtle. Parasitic on other diatoms. _Odontidium parasiticum_ Wm. Sm. Not common. Media (Palmer). In the constricted form it is known as F. construens var. binodis (Ehr.) Grun. Pl. 10, Fig. 35. An examination of the synonymy of the species of Fragilaria will convince the student of the difficulty of determining the correct name even in well-known forms. If all of the species of Fragilaria proper have granular chromatophores, and all of Staurosira are placcochromatic, a satisfactory division can be made, but so long as these facts are not known in all species, and as authors have repeatedly confused the two divisions, the nomenclature will be uncertain. F. harrisonii is probably in any case to be separated from the others. De Toni includes it under its original name of Odontidium, which genus he places near to Diatoma. The number of species in our locality is too limited to render further discussion of any value. {46}RHAPHONEIS EHR. (1844) (rhaphis, a needle) Frustule in zone view linear. Valve lanceolate or elliptical-lanceolate; pseudoraphe distinct; striæ radiating, moniliform. RHAPHONEIS AMPHICEROS EHR. Valve lanceolate, broad, with apices produced; striæ in curved lines, moniliform, the large granules in longitudinal lines. Blue clay. Pl. 10, Fig. 38. RHAPHONEIS AMPHICEROS VAR. RHOMBICA GRUN. Valve as in type form but shorter, with larger and more remote granules. Blue clay. Pl. 10, Figs. 39 and 40. RHAPHONEIS BELGICA VAR. INTERMEDIA GRUN. Valve lanceolate, rostrate; granules in longitudinal and nearly transverse, not radiating, lines. Absecon, N. J. Pl. 10, Fig. 41. DIMEROGRAMMA RALFS (1861) (dis, two, meros, a part, gramma, a letter) Frustules quadrangular, inflated at the angles, in fasciæ. Valve ovate or lanceolate; striæ moniliform, transverse or slightly radiate; median area or pseudoraphe broad, lanceolate.