THE DIATOMACE^E OF PHILADELPHIA AND VICINITY 45 



FRAGILARIA LINEARIS CSTR. 



Valve linear, with rounded apices; striae subtle; pseudoraphe indistinct. 



Marine. Cape May. 



PI. 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; striae, 17 in 

 10 p. 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; striae 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; striae subtle, 15 in 10 /x. L. of valve, 10-45 p. 

 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; striae 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 placco- 

 chromatic, 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. 



