892 SYSTEMATIC HISTOKY OF THE rNFUSORlA. 



G. insulare (E.), G. temdcolle (E.), 

 Australia; G. longicoUe (E.), Australia, 

 Asia, America; G. Jordani (E.), River 

 Jordan; G. obtmum (E.), Arabia, Ame- 

 rica; G. turritum (E.), Arabia; G. mu- 

 cronatum (E.), G. rhomhoideum (E,), | 



Asia ; G. 3Iosctmhicense (E,), Africa ; 

 G. Margaritaceum (E.), G. Savannce 

 (E.), British Guinea ; G. lanceolatum 

 (E.), America ; G. Palea (E.), fossil, 

 Jiu'a Moimtains, France. 



Genus SPHENOSIRA (E.). — Frustules united into a straight compressed 

 filament; lateral snrfaces with unequal extremities and a distinct central 

 nodule. Aquatic. The frustules in front view are scarcely cuneate ; and the 

 genus could be better placed in the IS^aviculeae, as indeed Kiitzing himself 

 suggests ; it seems to differ from them only in the unequal ends of the 

 lateral surfaces. 



Sphenosiha Catena (E.). — Frustules i what obtuse base. EA. p. 98, pi. 3. 1. 

 smooth ; lateral view with a mucro at | f. 27 ; KB. p. 88, pi. 29. f. 47. Mexico, 

 apex and a gradually attenuated, some- | (xi. 30.) 



FAMILY XYIIL— ]S"AyiCIJLE^. 



Frustules free, concatenate, or included in a more or less definite fi'ond ; 

 front view generally linear or quadi^angular ; valves with similar ends, a 

 median longitudinal line, and central nodule. " The Naviculeae frequently 

 resemble individuals in other families, but are to be distinguished by the 

 central nodule of the lateral surfaces, as well as by the regularity and 

 symmetry both of these and the front view " (Menegh.). In the minuter 

 forms the nodules are frequently very indistinct; when present, however, 

 they usually appear, in the front view, like a punctum at the middle of each 

 lateral margin. In doubtful cases this appearance will often aid in ascer- 

 taining their presence. 



* ErustuJes nude. 



Genus NAYICULA (Bory, Bab.). — Frustules simple, free, prismatic in front 

 view, rectangular laterally, with a longitudinal median peUucid line with 

 central and terminal nodules, Navicula was chvided by Ehrenberg into two 

 genera — Navicula with smooth, and Pinnularia with striated valves ; but 

 this division was not received by Klitzing or Brebisson, and is certainly un- 

 sound, as it assigns the species to each genus according to the power of the 

 author's microscope, whilst striae, we believe, are almost always, if not uni- 

 versally, present on the valves. The late Professor Smith reconstituted 

 Ehrenberg's genera, and made their characters depend on the presence or 

 absence of costae. These characters were far better than those of Ehrenberg ; 

 and were the costae always plainly developed as in Pinmdaria nohilis and its 

 allies, no difficulty could occur in determining the genera ; but in many of the 

 more minute species it is often very difficult to distinguish between striae and 

 costas. We have not admitted Pinnularia here, partly for the reason just 

 given, but principally because we cannot decide to which genus a large num- 

 ber of Ehi^enberg's species should be referred. 



slightly constricted at the middle and 



A. Valves more or less cotistricted at the 

 middle (Diploneis, E.). 



NAVicuiiA Americana (E.). — Turgid, 

 linear-oblong, with slightly constricted 

 centre and broadly roimded ends ; striae 

 wanting or indistinct. EM. pi. 2. 2. f. 

 16, New York and Rhode Island. 



N. Faba (E., K.). —Turgid, oblong, 



rounded at the ends, marked by longi- 

 tudinal lines ; strias wanting or indi- 

 stinct. = Di])loneis Faba, EB. 1845, 

 p. 365. River Tagus. The median line 

 interrupted by the central nodule ; three 

 lines on each side continuous. 



N. hyalina (E., K.). — Slightly con- 

 stricted at the middle, with oblong lobes, 



