72 P. T. CLEVE, SYNOPSIS OF THE NAVICULOIl) DIATOMS. 



where is a large foramen. The foramina form in the large rspecies, a more or less distiuct or 

 broad longitudinal hand across the striae. 



The central nodule consists of a conical silicious mäss, projecting in the inside of the cell, 

 usually excentric, so that one margin of its base (the median margin) coincides with the axis of 

 the valve. Between the nodules of both valves, in the interiör of the cell, is the median plasma- 

 mass, containing in its middle the nucleus. According to Otto Muller the central nodnle has, on 

 the top of the cone or its median side, an open shallow furrow, in both ends of which is a pore, 

 by which the plasma commnnicates with a system of closed channels in the central nodnle and, 

 by means of similar channels in the median line, with open fissnres in the parts of the median 

 line which are between the centre and the ends. From these pores pass vertically, throngh the 

 solid mäss of the nodnle, two channels (the channels of the central nodtile) which terminate on the 

 exteriör of the valve as two bulb-shaped pores (the median xiores). The channels of the central 

 nodule each give rise to two parallel, closed, channels, one above the other (the exteriör and in- 

 teriör channels). 



Two similar channels also open into the terminal nodnles. The exteriör of these channels 

 is at its end bent towards that side of the valve, on which the central nodiile is situated, and 

 terminates in an oblique, sometimes spirally twisted, fissnre (the terminal fissitre), which bends 

 ronnd the terminal nodule. The terminal fissures are in most cases turned to the same side, but 

 in some few cases in contrary directions. Their shape is somewhat different in different gronps, 

 sometimes curved and comma-like, sometimes straiglit, giving to the ends of the median line a 

 bayonet-like shape. 



On the lower side of the curved end, or opening of the exteriör channel, opposite to the 

 terminal fissure, is a triangulär fissure (the funnel) which passes obliquely through the terminal 

 nodule, and opens with its pore-like apex into the plasma-mass at the ends of the cell. The 

 median part of the funnel communicates with the interiör channel of the terminal nodule. 



The exteriör and interiör channels from the central to the terminal nodules are connected 

 by a fissure of more or less complicated structure. In many cases this fissure forms a filiform line 

 and seems then to be simply a vertical fissure. In other cases it is broad, and lies in an oblique 

 position. In some of the larger species the fissure is of a more complex nature, being formed by 

 the junction of short knife-like laminaj pi^ojecting from both halves of the valve. From the 

 half of the valve, on which the central nodvile is situated project three, in some cases two, such 

 laminse, alternating with two (or one) laminse from the other half of the valve. In some of the 

 larger species the anterior laminse on the half of the valve which contains the central nodule 

 cover the laminse on the other half of the valve on two portions of the median line, thus giving 

 rise to a biundulated median line. 



The genus Pinnnlaria comprises a great number of forms, both marine and fresh-water, the 

 latter being very predominant, forming an important and very characteristic part of the fresh- 

 water diatomaceous flora, both recent and fossil. The marine forms are not all closely connected. 

 One group among them is eharacterized by the peculiar form of the large terminal fissures, pro- 

 jecting from the ends of the median line at an angle of about 90". To this group belong P. Trc- 

 velyana, P. rectangulata, P. groenlandica, and in a less degree P. cruciformis. The latter seems to 

 be connected with P. guadratarea, having indistinct terminal fissures. Smaller marine forms bear 

 a great i'esGml)lan(;e to the smallest fresh-water Pinnularia' of the group Parallelistriata'. Among 

 the marine forms are a few more or less panduriform, which appear in several resjjccts to be 

 akiii to ])anduriform species of the genus Caloneis. 



The fresli-water forms pass into one another to a great extent, so that the definition of good 

 or (listinct species or groups is a matter of the greatest difficulty or almost impossible. Still, I 

 think some groups of foi'ms may l)e distinguislicd, although c]osp]3' connected with eacli other. 

 Such groups are the following: 



