16 THE DIATOMACE^ OF PHILADELPHIA AND VICINITY 



Marine and brackish. Common in all parts of the world, and fossil in the Miocene. 

 The Philadelphia form is the var. genuina Grun. 



PI. 1, Figs. 11 and 12. 



In a gathering from Media of Meloseira crenulata (Palmer leg.), occasional filaments 

 are noticed with much longer and narrower frustules which become enlarged in the middle 

 and are seen to contain inner frustules in the process of still further division, as shown in 

 Fig. 2, PI. 38. 



Meloseira dickei Thwaites shows internal box-like cells placed one within the other, 

 which were supposed by Thwaites to be a method of reproduction. Wm. Smith doubts 

 this, but is unable to offer any explanation. In the present form the mode of reduplication 

 is that usually found in filamentous forms, but in this case the presence of perfect frustules 

 enclosing others in the process of still further division has been heretofore unfamiliar to me. 

 The swelling in the middle appears to indicate that not all filamentous diatoms are reduced 

 in size by subdivision. In outline the valve is like that of a "truncated cone, " as described 

 by Petit in referring to Gaillonella granulata var. bambusina Petit (Diat. Nouv. et Rares, 

 Jour, de Micrographie, 1890). 



GAILLONELLA BORY DE ST. VINCENT (1823) 

 (named after Gaillon, a botanist of Dieppe) 



Frustules ellipsoidal, united in long filaments, usually found in pairs; each valve is 

 furnished with a circular collar or crest extending at right angles to the convex edge. Valve 

 hyaline at the centre from near which radiate lines of fine puncta, 18-20 in 10 p. 



NOTE. The original names of both Meloseira and Gaillonella are retained, as there is 

 no good reason for contracting the Greek diphthong in the first, and the second is the 

 correct spelling. 



GAILLONELLA NUMMULOIDES (DILLW.) BORY 



Frustules as in the generic diagnosis. Diam. 30 M- 



Conferva nummuloides Dillwyn (Brit. Confervae, p. 45, Sup. PI. B). 



Meloseira nummuloides Ag. 



Heiberg and O'Meara assign this species to Lysigonium moniliforme (Muell.) Link, 

 which is not keeled. While Dillwyn's and Lyngbye's figures do not show the keel, it is 

 probable from their descriptions that the angular outline produced by the keel was noticed. 



Marine or brackish. Coast of New Jersey; Hudson River (Bail.). 



PL 1, Figs. 13 and 14. 



Gaillonella moniliformis of Bailey is this form, as he describes it as having "two minute 

 projections of the delicate transverse ridges seen near the ends of the two globules belong- 

 ing to a joint. " (Amer. Jour. Science, 1842, p. 89, PI. 2, Fig. 3.) 



LYSIGONIUM LINK (1820) 

 (luo, to loose, and gonu, a joint) 

 Frustules globose, concatenate; valve simply punctate. 



LYSIGONIUM MONILIFORME (MUELL.) LINK 



Frustules usually in twos, not keeled; valve with puncta hi longitudinal lines, the 

 puncta of the enveloping zone larger and in transverse rows. L. 25-40 M (De Toni). 

 Conferva moniliformis Mueller (1783). 



