NAV1CULA. 22 1 



dilated transversely round the central nodule, which is placed somewhat 

 obliquely ; terminal nodules robust. Strice fine with elongated puncta, about 

 1 6 in i c.d.m, subparallel, somewhat oblique, interrupted near the margins 

 by a deep sulcus, which terminates at the anterior part of the terminal nodules. 

 Length, to to 17 c.d.m. Breadth, 2^25 to 3 c.d.m. 



Fresh water. Pleinevaux (Delogne), Ard. Lieg. (De Wild.). England, Ireland, Germany, 

 Finland (Cleve), etc. 



var. amphigomphus Ehr. (H.V.H. Atl., pi. 13, f. 2* ; in Type 

 No. 67), plate 5, fig. 213. 



Smaller, with cuneate apices. 



Fresh water. Ard. Lieg. (De Wild.). England, Ireland. 



var. firma Kutz. (in H.V.H. 's Type No. 67). 



Differs from the preceding form in the apices, being rounded and not 

 cuneate. All intermediate forms are found in the same gathering. The 

 striae (in Type No. 136) have otten an oblique direction. 



Fresh water. This variety as well as the following are found here and there throughout 

 Europe. 



var. amphirhynchus Ehr. (H.V.H. Atl., pi. 13, f. 5*), plate 5, 

 fig. 214. 



Valve linear, narrow, with apices broadly and longly rostrate, rostrum 

 slightly inflated at the apex. 



Fresh water. 



var. dubia Ehr. (H.V.H. Atl. Supp., f. 32* ; in Type No. 79), 

 plate 5, fig. 215. 



Valve linear, short, rather broad, with apices broadly rostrate, rostrum 

 not inflated. 20 striae in 1 c.d.m. Length, 375 c.d.m. Breadth, about 

 1 c.d.m. 



Fresh water. La Hulpe (Del.). 



var. undulata Grun. (H.V.H. Atl., pi. 13, f. 6*), plate 5, fig. 

 216. 



Differs from the amphirhynchus in its margins being tri-undulate. 



Fresh water. Rather rare? Antwerp. 



var. affinis. (H.V.H. Atl., pi. 13, f. 4*; Type No. 136), plate 5, 

 fig. 217. 



Valve linear, with apices more or less rostrate capitate. 



Fresh water. 



var. producta. (H.V.H. Atl., pi. 13, f. 3*), plate 5, fig. 218. 

 Valve elliptic, with apices strongly rostrate capitate. 



Fresh water. 



Many of these forms are often met with together. The Revd. P. A. Gautier 

 has observed that in all these forms, after death, the endochrome divides into 

 four parts ; during life the commencement of a division can even be observed 

 in the middle of the endochrome. N. Iridis and its various forms constitute 

 the genus Neidium of Messrs. Pfitzer and Cleve. 



