156 



HAllDWICKE'S SCIENCE-GOSSIP. 



[July 1, 1867. 



JOVA 





MONMOUTH DEPOSIT. 



BEPORE proceeding with the description of the 

 diatoms detected in this deposit, I would ob- 

 serve that no truly accurate description can be given 

 of forms occurring in fossil deposits unless they 

 have been previously studied in the living state. 

 Dr. Lewis, in the proceedings of the Academy of 

 Natural Sciences of Philadelphia, January, 1865, 

 quotes some remarks of Professor H. L. Smith, who 

 has long studied the habits of the living Diatomacese. 

 He says,—" When I find Navicula amphirhynchus 

 conjugating and producing Navicula firma, Stauro- 

 neis gracilis producing Stauroneis Phnenicenteron, 

 Surirella splendida producing Surirella nobilis, 

 quite different in form and striation, I cannot but 

 doubt the propriety of making new species out of 

 every different shape and marking." 



In addition to the forms 

 already indicated (pp. 133), 

 I have met with the follow- 

 ing : — Navicula firma (Kut- 

 zing), "valve large, turgid, 

 oblong, lanceolate, with ob- 

 tuse cuneate apices, thick- 

 ened borders, large median 

 nodule, striae wanting or 

 obscure." The median no- 

 dule of Kutzig is rather a 

 large blank space, accom- 

 panied by a slight thicken- 

 ing of silex, than a nodule ; 

 the striae are transverse, 

 delicate, and about 40 

 100. 



\\ 



m 



Fig. 151. Navicula firma, var. R 

 (Navicula dilatata, Ehr.) x 400. 



Fig. 152. Navicula firma, 

 var. y, x 400. 



Variety a, linear oblong = Navicula Iridis, Ehr. 



Variety /3, pointed elliptic = Navicula dilatata, 

 Ehr. (fig. 151, outline only). 



Variety y, cuneate = Navicula amphigomphus, 

 Ehr. (fig. 152, outline only). 



Variety £, valves turgid elliptical-lanceolate, with 

 several marginal longitudinal bnes, large median 



blank space, striae distinct. This is undoubtedly 

 the finest of all the varieties of Navicula firma. 

 Eig. 153, valve. Eig. 153 a, b, ideal sections of 

 valve and frustule ; a represents a central transverse 

 section, showing thickening of the silex forming the 

 blank median space; b, transverse section of frustule 

 beyond the median space, and intended to illustrate 

 the contour of the frustule : it will be seen that one 

 portion of the valve inclines downwards towards the 

 median line, and the other, or marginal part, forms 

 a broad curve towards the connecting zone. 





_ 



153. Navicula firma, var. 0, d x 400, c x ],O0O. 



Eig. 153 c represents a small part of a valve magni- 

 fied 1,000 diameters, showing that the appearance of 

 longitudinal lines is produced by the greater 

 distance of the striae on that portion of the valve. 



I 



■W 



Fig. 154. Navicula Fig. 155. Navicula Fig. 156. Navicula 

 bacillum x 400. serians. serians, var. |3 x 800. 



Navicula bacillum (Ehr.), Valves linear, with 

 truncate rounded apices, terminal and central 

 nodules distinct, striae parallel, delicate, about 50 in 

 100, not reaching the median line (fig. 151). Navi- 

 cula bacillaris of Dr. Gregory was supposed to be 

 identical with this species ; but a careful examina- 

 tion shows them to be distinct. It is rare in the 

 lighter parts of this deposit. 



