70 THE DIATOMACE^E OF PHILADELPHIA AND VICINITY 



GOMPHONEIS HERCULANEUM (EHR.) CL. 



Valve clavate, with rounded apex; costae, 13 in 10 n, alternating with double rows of 

 fine puncta, 22 in 10 ju, in oblique rows; axial area narrow, central area rounded, with one 

 stigma. 



Gomphonema capilatum Ehr. var. herculaneum Ehr., H. L. S., Type Slide No. 177. 



Common in the blue clay. 



PI. 19, Fig. 2. 



PI. 38, Fig. 15, zone view of young frustule. 



GOMPHONEIS MAMILLA (EHR.) CL. 



Valve lanceolate, with rounded apex and base; striae costate, 10 in 10 n, alternating 

 with double rows of fine puncta; axial area linear, sometimes oblique, central area small, 

 with one or more stigmas. 



Blue clay. Rare. 



PI. 19, Fig. 1. 



In one frustule I noticed one valve with one stigma and the other with four stigmas. 



The difference between G. mamilla and G. elegans is not very great. In the latter the 

 central area is larger and the longitudinal lines not so near to the margin. The stigmas 

 form a circlet. There appears to be a coincidence in the relation of Gomphoneis to Gom- 

 phonema, and that of the true Achnanthes to the group described by Cleve under Achnan- 

 thidium. In Gomphoneis and Achnanthes the striation is both costate and punctate 

 while in Gomphonema and Achnanthidium the striation is punctate only. 



GOMPHONEMA AG. (1824) 

 (gomphos, a peg, and nema, a filament) 



Valve elongated, asymmetrical with respect to the transverse axis; striae transverse, 

 usually radiate, punctate. 



Cbromatophore band single, the middle lying on one zone. 



In conjugation, according to Thwaites and Pfitzer, from two mother cells, which do 

 not form a positive union, two auxospores are developed parallel to the original frustules. 

 In Plate 19, Fig. 19, I have drawn a representation of the auxospore formation as I have 

 frequently observed it in a gathering sent me by Mr. T. C. Palmer, containing G. angus- 

 tatum, a common species in this locality. The sagittal plane of the valve of the auxospore 

 is at right angles to the plane of the valve of the mother cell. Two valves of one of the 

 mother cells are seen separated, one on each side of the auxospore which is nearly twice 

 the length of the original frustules. The two valves of the other mother cell are not shown 

 as they are not usually found closely united. In the figure one valve alone of the auxo- 

 spore is seen, the opposite valve not being in focus. The valves of the auxospore are usually 

 more or less arcuate, as in Cymbella, to which the genus is closely allied. 



Grunow divides Gomphonema into two groups, Asymmetricae and Symmetricae, 

 according to the presence or absence of stigmas. Cleve suggests Stigmaticae and Astigma- 

 ticae as more suitable in order to agree with the Cymbellae. The Stigmaticae are found 

 chiefly in fresh water, sometimes in brackish. All of the marine forms belong to the Astig- 

 maticae, which, however, include some common fresh-water forms. Many species of 

 Gomphonema are stipitate, some occur in gelatinous masses, and others are free. 



