NAVICULA. 2 I 5 



There is shewn in fig. 193, on the right moiety of the specimen, the 

 fine striae which only exist on the surface of the valve, and on the left 

 robust stride, strongly radiate, which are found in a deeper layer, probably 

 on the interior surface of the valve. 



Mixed with the type form, but rare. Louvain and Manage (P. G. ). 



Note. The forms above described were included by my late excellent 

 friend Mr. de Brebisson in his genus Van Heurckia. The examination which 

 I have made with better objectives than those in existence at the time de 

 Bre'bisson published his Work, has convinced me that the raphe is simple, and 

 that therefore these forms cannot be included in the said genus. 



XIII bis. Fusiformes. 



N. fusiformis Grun. (M.M.J., 1877, xviii., p. 178, pi. 195, f. n*) 3 

 plate 27, fig. 768. 



Valve narrowly lanceolate, infinitesimal])' attenuate up to acute apices. 

 Transverse stria?, 33 in 1 c.d.m. Longitudinal striae, 36 in 1 c.d.m. Raphe 

 thick, very distinct, central nodule indistinct. Length, 11 to 15 c.d.m. 



Marine. Hitherto only found in Honduras. 



var. ostrearia (Gaill.) H.V.H. (JV. fusiformis vcr. ostrcaria 

 Grun. in H.V.H. Syn., pi. 14, f. 33*). plate 27, fig. 769. 



Valve small ; transverse striae, 36 in 1 c.d.m., excessively delicate, 

 scarcely visible. Length, 6*25 to 7^25 c.d.m. Breadth, 6 to 7 mill. d.m. 



Marine. North Sea. Sweden and probably other places. 



This form lives in oyster beds and colours the oysters green. 



By the side of N. fusiformis are placed two forms not very well known, 

 which Prof. Cleve includes in his group Navicular Entoloice and which are 

 distinguished from the Fusiformes by their lanceolate axial area. They 

 are : 



N. inornata Grun. (Arc. Diat., p. 124, pi. 3, f. 56*), plate 27, 

 fig. 770. 



Valve fusiform, convex. Striae delicate, almost parallel, 19 to 21 at the 

 middle of the valve, 23 or 24 in 1 c.d.m. at the apices, leaving a longitudinal 

 area, narrow, lanceolate, and appearing to be crossed by two longitudinal 

 lines, which however are illusory. Length, 5 to 9 c.d.m. Breadth, about 1 

 cd.m. 



Marine. English Channel. Finmark. Bahusie. 



